that chemical substances formed during pregnancy in the tissues of the fœtus will, if introduced into the maternal blood, directly evoke the appropriate activities of the remote mammary glands.1

These are only a few instances of a class of mechanisms, strictly chemical in character, by which the activities of remote and dissimilar organs are automatically coordinated; a further class of such mechanisms, although involving a chemical substance conveyed by the blood, carries out the actual regulation by means of the central nervous system. An example of this class is afforded by the researches of Haldane and Priestley upon the carbonic-acid gas in the pulmonary air. These show that the alveolar pressure of carbonic acid in the lung spaces remains constant even when the atmospheric pressure is considerately altered in amount. The constancy is due to the circumstance that the respiratory nerve centres are exquisitely sensitive to a rise in this carbonic-acid pressure. Any such rise slightly augments the carbonic-acid tension of the pulmonary blood, which, on being conveyed to the nerve centres, arouses their greater activity, and the increased efficiency of the respiratory ventilation, thus produced, rapidly reduces the amount of the very agent which is its exciting cause. The researches of Hill and Greenwood, with air pressures up to seven atmospheres, bear out the conclusion that by this automatic mechanism the air in the lung alveoli has a practically constant pressure of carbonic acid in any given individual.

The introduction, in this example, of the respiratory centres and nerves raises the question whether the nervous system, which is in a very special sense the channel for the regulation and coordination of the various activities of the body, may not itself be conceived to be a supreme example of an automatic physico-chemical mechanism, the transference from one part to another taking place, not through the flow of blood containing chemical substances, but through a more subtle physico-chemical flow along the highly differentiated nervous strands of which this system consists. The nervous system is not popularly regarded in this light; on the contrary it is considered to be the special seat of vital directive forces, and it is held, even by some scientific men, that the nervous energy which it manifests is so transcendental in its essence that it can never be brought into line with those modes of energy prevailing in chemistry and physics. There is, moreover, a widespread belief, founded upon conscious volitional power, that nervous energy can be spontaneously created, and that even if its manifestations are bound up with the integrity of certain definite nervous structures, these structures only form the material residence of genii, temporarily in possession, endowed with the powers of hypothetical homunculi at the bidding of which the manifestations either take place or cease." 4

The complexity of nervous structure and the apparently uncertain character of nervous activities furnished the older writers with plausible reasons for assuming the existence of animal spirits, but the extensive researches of half a century progressively suggest that nervous phenomena may be regarded as the sum of particular physico-chemical processes localised in an intricate differentiated structure, the threads of which are being unravelled by neurological technique. This chapter of physiology still bristles with difficult problems and obscure points, yet the unmistakable trend of the immense advances which have been made in recent years is towards the assumption that nervous processes do not in their essence differ from processes occurring elsewhere in both the living and non-living worlds.

As regards structure it is generally assumed by neurologists that the whole system is a fabric of interwoven elements termed neurons, each with a nucleated nerve cell and offshoots, one of which may be extended as a nerve fibre, whilst no nerve fibre exists which is not the offshoot 1 Starling and Lane-Claypon.

2 Haldane and Priestley, "The Regulation of Lung Ventilation." Journ. of Physiol.. xxxii. 1905.

3 Hill and Greenwood, "The Influence of Increased Barometric Pressure on Man." Proc. Roy. Soc., vol. lxxvii B, 1906, p. 442.

Lodge, "Life and Matter" (London: Williams and Norgate, 19:6). "Matter is the vehicle of mind, but it is dominated and transcended by it (p. 123). "Contemplate a brain-cell, whence originates a certain nerveprocess whereby energy is liberated with some resultant effect" (p. 168). "It is intelligence which directs; it is physical energy which is directed and controlled and produces the result in time and space" (p. 169).

of one such cell. This neuron theory is based upon developmental history and upon the suggestive fact that each nerve cell forms an independent trophic centre for its own distributed processes. It is undoubted that, like the atomic theory in chemistry, the neuron theory has proved of enormous service, enabling neurologists to disentangle the woven strands of nerve-cell processes even in such an intricate woof as that of the central nervous mass. There are, however, difficulties associated with its full acceptance in physiology, as indeed there are said to be in connection with the full acceptance of the atomic theory in chemistry; but dismissing these for the moment, I pass on to consider the presumable character of such a conception of nervous activities as would be demanded on the sup position that the nervous system is, as regards all essentials, an automatic physicochemical mechanism.

In the nerve fibres, which are undoubtedly the offshoots of nerve cells, the only demonstrable changes during the actual passage of nervous impulses are of an electrical type. These resemble the effects which would occur it there were redistributions of such electrolytes as are known to exist within and around the differentiated fibrillated core or axon of each nerve fibre. All the better-known aspects of nerve-fibre activities are in accordance with such an electrolytic conception. The exquisite sensibility of nerve to physical and chemical changes of a sudden character would be associated with the fluctuating and variable character of electrolytic distribution, this instability being characteristic of particular electrolytes in colloidal solutions; hence physical and chemical alterations primaria affecting the nerve envelope will, by modifying the electrolytic distribution, produce physico-chemical change in the internal axon itself. Such changes, when once produced at any point in the differentiated fibrillar continuum of the nerve fibre, must in accordance with the conception first propounded by Hermann be propagated or transmitted along this continuum. The redistribution of electrolytes at the seat of the external impression being itself a source of electromotive effects, electrical currents demonstrably flow from this point into the contiguous parts of the fibrillar continuum. Such flow of current must reproduce in this neighbouring continuum that electrolytic redistribution which is the fundamental aspect of nerve-fibre activity. Thus, by this comparatively simple automatic mechanism. the physico-chemical electrolytic change is successively assumed by the various portions which compose the length of the differentiated axon, and the new or active phase is propagated along a nerve fibre as infallibly as a flame speeds along a fuse when one end is ignited; in this was the conception explains how a so-called nervous impulsis brought into being. Further, the brief duration of the activity of the nerve, its rapid development and slowe decline, and the circumstance that a second external chang cannot arouse a second activity if it occurs very shortly after an effective predecessor, all have their counterpar on the electrolytic side, and we have convincing evidence that the electrolytic redistribution during activity cannot be again produced until the electrolytic condition has mor or less returned to its original resting poise: the rea! peculiarity of the living tissue is its persistent tenden to re-establish the electrolytic concentration of this resting poise.1 Finally experiments show more and more eit vincingly that the capacity of the nerve to respond te external changes, as well as the magnitude and duration of the aroused activities, are particularly suscept ble modification by all those agents which are most petent in affecting electrolytic aggregates, such as temperatur electrolysis, and impregnation with various electrolytes

These electrical indications of nerve-fibre activities ar fundamentally the same whether the fibres occur in pr pheral nerve trunks or in the bundles which course through the central masses; and thus, if the whole system consisted of nothing but the united strands of differentiate nerve fibres, nervous phenomena would be merely the es pression of the development, along appropriately distributed tracts, of similar electrolytic changes primarily started b some external physical or chemical alteration. But addi tional complications are introduced by the existence d nerve-fibre endings and by the interposition of the nerve

1 Gotch and Burch, Journ. of Physiol., vol. xxiv. 1899, p. 470

which bears no relation to that of the centripetal ones. But it must be remembered that even in nerve fibres it is possible for a succession of stimuli to evoke a different succession of electrolytic changes and of nerve impulses, provided that some of the successive stimuli fall within the period of inexcitability which occurs during the establishment of each new electrolytic poise.' We have, therefore, only to assume, as is very probable, that in the central portion of the nervous path this poise is prolonged in its development, and numbers of centripetal impulses must necessarily fail; hence the emergent ones will have a special periodicity indicative of the duration of the swing of the electrolytic rearrangement which occurs when the synapses plus the cells are traversed by the entering impulse.

The second feature which more particularly suggests spontaneous cellular activity is the well-known fact that reflex centrifugal discharges may continue after the obvious centripetal ones have ceased. This is preeminently the case when the central mass is rendered extremely unstable by certain chemical compounds, such as strychnine, &c. There are, however, suggestive indications in connection with such persistent discharges. The more completely all the centripetal paths are blocked by severance and other means, the less perceptible is such persistent discharge, and since nervous impulses are continually streaming into the central mass from all parts, even from those in apparent repose, it would seem that could we completely isolate nerve cells, their discharge would probably altogether cease. In this connection a suggestive experiment was carried out some years ago upon the spinal cord of the mammal. A portion was isolated in situ by two crosssections, and a part of this isolated cord was split longitudinally into a ventral half containing the motor or centrifugal nerve cells and a dorsal half containing the breaking up of the centripetal nerves; each half was then examined for those electrolytic changes which indicate the presence of nervous impulses. It was found that, even in the strychnised animal, no electrical effects could be detected in the ventral half of the cord or its issuing roots, although such effects were marked in the whole cord, and occurred in the dorsal half which contained the centripetal nerve fibres.

This experiment indicates that even in the hyper-excitable condition produced by strychnine the spinal motor nerve cells did not discharge centrifugal impulses when cut off from their centripetal connections. It is corroborated by the results obtained by Baglioni in the frog and small mammal, and, taken in connection with those previously mentioned, it affords considerable foundation for asserting that the chief rôle of the nerve cell is trophic, and that, as regards issuing nerve impulses, it only forms a modified part of the conducting path. The more we investigate the physiology of the nervous system, the stronger becomes our belief that for centrifugal discharges to occur centripetal impulses must be primarily started either in the peripheral sensory surfaces by changes of a physical or chemical type occurring in the external world, or at some point in the nerve continuum by local chemical or physical changes within the body, especially those due to the chemical condition of the blood. Having been thus started they course along definite structural paths, and the only direct indications of this passage consist of such phenomena as would be produced by the redistribution of concentrated groups of electrolytes-a purely physicochemical process.

This conception places the propagation of the nervous excitatory state as the sole determining factor of nerve activities, central or peripheral. It derives additional support from the circumstance that it is in harmony with that aspect of these activities which is comprised under the term, inhibition. Any effective regulating system must be able to bring into play both incentive and restraint-the whip and the reins. The possession by the central nervous

1 Gotch and Burch, Journ. of Physiol., vol. xxiv. 1899, p. 410: Boycott, Journ. of Physiol., vol. xxiv. 1899, p. 144; Buchanan, Journ. of Physiol., vol. xxvii 1901, D. 98. &c

2 Gotch and Horsley, Phil. Trans., vol. clxxxii. pp. 267-526. (London,

181)

3 Baglioni, Archiv f. die Ges. Physicl., 1000, Supplement, pp. 193-242. (Leipzig.)

mechanism of inhibitory powers is remarkable both for its extent and its delicacy. It appears more and more prob able that this is achieved by the propagation of nervous impulses of the ordinary type. Thus, recent researches by Sherrington show that the propagated impulses from a given central mass may, although normally inhibitory to the centrifugal discharge of another mass, become directly incentive if the second controlling centre has its excitability abnormally augmented by strychnine, tetanus toxin, &c.' As regards their fundamental characters it thus appears that both augmenting and inhibiting impulses belong to the same category. Moreover, such theories of central inhibition as embrace all the phenomena involve as their essential basis the cutting-off of the potent centripetal supply to the inhibited centre. In the interference theoty this cutting-off is assumed to be caused by the arrival of other nerve impulses which, breaking into the path of normal centripetal flow, obstruct and run counter to this potent stream. In the ingenious drainage theory, propounded by McDougall, the cutting-off is an indirect one, ic being assumed that the new stream enters other sidechannels, and thereby opens up a short circuit through which the potent ones drain away without reaching the centrifugal centre. Even Langley's conception of receptive substances played upon by impulses must be associated with a check in the efficiency of the continuous centripetal supply.

From the foregoing it appears that the physiologist has definite grounds for believing that, as far as present knowledge goes, both the production and cessation of central nervous discharges are the expression of propagated changes, and that these changes reveal themselves as physico-chemical alterations of an electrolytic character. The nervous process, which rightly seems to us so recondite, does not, in the light of this conception, owe its physiological mystery to a new form of energy, but to the circumstance that a mode of energy displayed in the nonliving world occurs in colloidal electrolytic structures of great chemical complexity. There is a natural prejudice against the adoption of this view, but such prejudice should surely be mitigated by the consideration that this full admission of physiology into the realm of natural science, by forcing a more comprehensive recognition of the harmony of Nature, is invested with intellectual grandeur.

With such questions as the essential meaning of consciousness and the interpretation of the various aspects of mind revealed by introspective methods, the physiologist, as such, has no direct concern. For his purpose states of consciousness are regarded merely as signs that certain nervous structures are in a state of physiological activity; and he thus limits the scope of physiology to the objective world. This limitation of physiology does not prohibit a treatment of the subjective world along lines calculated to display that intellectual causative array which characterises science; it merely indicates that this particular application of scientific method is not physiology, but that something else, still more profound, which is now termed psychophysics.

66

But if objective phenomena form the subject-matter of the physiologist, then the legitimate materialism of science must constitute his working hypothesis; and his well-defined purpose must be to adapt and apply the methods of physics and chemistry for the analysis of such phenomena as he can detect in all physiological tissues, including the nervous system. The trend of such a strictly physiological analysis is towards a conception in which the highest animal appears as an automaton composed of differ. entiated structures exquisitely sensitive to the play of physical and chemical surroundings.2 The various parts the animal body are linked by circulating fluids and by one special structure, the nervous system; in this linking of parts the physiologist detects the working of automatic chemical mechanisms of great delicacy which, once de veloped, are retained and perfected in proportion as they efficiently regulate the various bodily activities and coordinate them for the welfare of the whole organism. The

of

1 Sherington, Proc. Roy. Soc., vol. lxxvi B, pp. 269-297. (London, 1905.)

2 See Huxley, "On the Hypothesis that Animals are Automats Evening Address. Brit. Assoc, Belfast, 1874. Re-published in "Collected Essays," vol. i. (Macmillan, 1904.)

plastic nature of nervous tissue renders it, in accordance with the principles of natural selection, particularly favourable for progressive change in this direction, and thus developments may occur which reach their highest physiological expression in the brain of man.

In conclusion, attention may be drawn to the peculiar instability of living processes and structures. The living units show that significant mutability which the physiologist describes as metabolism. This mutability appears to be encouraged or discouraged by the extent to which it fulfils a purpose, and this purpose in a living organism is the dominating law of its own development. The fulfilment of this purpose by means of physical and chemical change is such a general characteristic of living processes that a physiologist may with some confidence suggest that this fulfilment is the distinctive mark of a living thing.

SECTION K.

BOTANY.

these forms have remained too long a thing apart. Haberlandt and Goebel have shown us-to name no others-how happy is the hunting-ground which the Bryophytes provide. Further work is still required, directed more especially to certain important points in the life-history.

With the regular vascular cryptogams the relations between the stages are of course different. Here we find large complex sporophytes holding the ground, but hampered by the ever-recurring necessity of dependence upon outside water for the performance of the reproductive process.

The land problem was solved on ingenious lines. The differentiation of gametophytes which accompanied heterospory rendered possible the retention of the larger spore and female prothallus. Thus retained aloft, the drawback of the double existence is overcome and the advantages of the elaborated sporophyte more fully realised. The water conditions are brought directly under the plant's control through the device of the pollen-chamber, and the way paved for the ideal seed with siphonogamy.

The Seed, a Chapter in Evolution.

As the subject of the first portion of my Address I propose to consider the place of the seed in the evolutionary history of plants. The seed-character is the distinctive mark of three great groups of plants-the Pteridosperms, Gymnosperms (including Cordaite), and Angiosperms. Nor will it be seriously questioned that the possession of this organ has given supremacy to seed-bearing plants over groups not thus characterised in a majority of the types of environment where vegetation is able to exist. Exceptions, of course, there are, though few of them are wholly immune from the invasion of the Spermophyte. The sort of habitat, for instance, in which Zostera flourishes-sometimes to the exclusion of other forms-is held more as a result of vegetative aggressiveness than in virtue of any special power conferred by the seed-habit.

Our stock of knowledge of those plants which had attained to the seed-bearing condition in a bygone age has undergone some extension during the last few years; the seed, too, has shed its glamour over other branches of morphological inquiry, so that no serious apology is necessary for its selection as the subject of this morning's discourse.

It is generally conceded that the primitive vegetation arose in the waters, and that with the parting of the waters and the emerging of land and continents this primitive stock of plants was sufficiently plastic to take advantage of the new conditions, throwing up successive hordes which effected a footing on the land, and in time peopled the whole earth with forms adapted to the varying habitats and climates as they differentiated.

Of the character of these primæval aquatic types no direct information has been vouchsafed. It is a matter of inference that they possessed much in common with the green Alga of to-day, which, living in a biologically stable medium, are commonly regarded as their nearest representatives. Be that as it may, the complexity of the lifehistory of existing Algæ and the frequent presence of neutral generations seem significant of the capacity of their progenitors to originate forms with sporophytes adapted to terrestrial conditions.

In our Liverworts and Mosses on the one hand and the Ferns and their allies on the other, two divergent evolutionary lines are represented, both fitted to existence upon land surfaces, but handicapped by the retention of a nonterrestrial method of effecting the sexual process. In the Bryophytes the physiological continuity and dependence of the sporophyte upon the gametophyte is preserved throughout, and it never rises above the status of an elaborate spore-capsule; whilst the gametophyte, though often reaching a complex vegetative differentiation, offering many analogies with the sporophytes of higher plants, is condemned to pigmy dimensions through the incubus of the inherited aquatic mechanism of fertilisation.

Though remote from the series that have culminated in seed-plants, the Bryophytes are a group offering many an instructive parallel with the main series of plants; certainly

All the elements of the seed were present before, but virtually a fresh stage intercalated in the life-history. Further elaboration came bit by bit as the possibilities were successively realised. With the evolution of the seed, the plant rose at a bound to a higher plane, and this structure in its perfected form has become the very centre of the plant's existence.

The case of Cycas and Ginkgo with motile sperms affords an extreme demonstration of the inertia of heredity, the persistence in living seed-plants of the original aquatic flagellate type.

Obsolete as they are and faced with extinction, these survivors from the middle epoch of the world's history still hold their ground in a few scattered localities. In this connection we shall listen with interest to Prof. Pearson's account of the Encephalartos-scrub of South Africa which is to occupy us during the course of the present sitting of the Section.

How the sperms became replaced ultimately by the passive cells of the pollen-tube we have no knowledge.

If the conjecture be well founded that the change came late rather than early, then the conservatism of the spermophytic line in this respect stands in marked contrast to the adaptability that is so characteristic of another phylum of aerial plants. The ready evolution of siphonogamy in the form of fertilising tubes, so common in the Fungi, perhaps finds its explanation in the close filiation of this group with primitive and plastic forms. The fertilising tube may reasonably be regarded as a special case of a general susceptibility to chemiotactic stimuli which distinguished the whole hyphal complex of the group from very early times. In the case of the spermophyte, on the other hand, the motile spermatozoid seems to have persisted through a long and complicated ancestral history, so that its elimination may have been less easy of achievement.

The seed, once evolved, became the centre of a host of accessory organs, constituting what we know collectively as the fruit and flower. By these it has been robbed, as we shall see, of many of its pristine functions, and at the same time has undergone marked structural reduction. In the highly elaborated Angiosperm more especially we find an almost stereotyped uniformity in seed-structure contrasting with an infinite diversity in the outward floral

husk.

In attempting a sketch of the origin of the seed one has to admit at the outset that recent discoveries bring us no nearer to its prototype than we were a decade ago. For the seeds of the Pteridosperms are advanced structures recalling quite vividly the type long familiar in living Cycads. It would be overstating the case to say they have nothing primitive about them, but there is a long chapter in evolution to be deciphered before we can connect, say, the seed of Lyginodendron with the sporangium of any Fern at present known to us.

The great interest of the recent correlation of seeds with Coal Measure plants lies less in the structure of these correlated seeds than in the very extensive series of plantremains which we have thus come to recognise as belonging to the earlier Spermophytes.

For the position of these plants had remained in suspense.

The elaborate anatomical investigation which their vegetative organs had received at the hands of Williamson, Scott, Solms-Laubach, and others showed them to occupy a transitional position between the Ferns and Cycads. In certain respects they showed an advance in the cycadian direction, whilst in others they were wholly fern-like. Their fructifications were unknown, and their nature remained an open question. It was for this group, or series of transitional groups, that Potonié proposed the appropriate name of Cycadofilices.

We know now that the Lyginodendreæ and Medulloseæ bore seeds attached to their fronds. The seeds have been found attached in some cases to reduced fronds consisting of a branching rachis, in others to fronds of the normal filicinean type. Indeed, so far as habit is concerned, these plants may rightly be described as seed-bearing Ferns. As such, indeed, most people will be content to regard them as forms, that is, having close filicinean relationship in which the reproductive method has been profoundly modified, the internal anatomy to a less extent, and the habit hardly at all. Had these Pteridosperms come to light during the lifetime of Hofmeister that master of morphology must have pounced upon them as furnishing an important link in his chain. These fossils and the spermatozoa which the Japanese botanists discovered in the seeds of Cycas and Ginkgo, indeed, afford the most convincing direct evidence of the soundness of the Hofmeisterian scheme that it is possible to conceive. Nor is that all. For by confirming the indications first revealed by the earlier investigation of the vegetative anatomy, the Pteridosperms have afforded us a striking object-lesson of the value of the anatomical method of the significance of purely anatomical characters too long ignored by the systematist.

Not so long ago, when new examples of these Pteridosperms were turning up on every hand, some pessimists were inclined to wonder whether, after all, any groups of real Ferns existed in the Palæozoic rocks. Such sporangia as were known might well be the pollen-sacs of seed-bearing plants. All doubts on this score are happily set at rest by the detection of germinating Fern-spores in contemporary beds. Nor can I think of any more fitting tailpiece to the investigations which lead the way to the Pteridosperms than the discovery, by the same investigator. of the antidote to these rather disturbing views. However, it is needless to dwell further on these matters now, in view of Dr. Scott's address to-morrow upon the Present State of Palæozoic Botany.

Be

But to return to the history of the seed. In the absence of direct evidence, one can only conjecture that some old generalised type of sporangium formed its prototype, something substantial, on the lines of a Botryopteris or Zygopteris, perhaps. The heterospory that was the precursor of the seed-like condition must have been a transient phase, or else it is lost in the pre-Carboniferous obscurity. that as it may, the passage from the dehiscent to the indehiscent monosporal megasporangium finds its analogy in every group of plants. Where there is extreme numerical reduction of the contained structures- -be they spores or seeds-a multitude of cases in the Fungi, in the Algæ, and the angiospermic flowering plants show that dehiscence tends to become obsolete. The failure to dehisce does not appear to be directly correlated with any mechanical difficulty in ejaculation. It is more probably one of those obscure cases of interdependence of phenomena in which the vegetable kingdom abounds. A special investigation directed to the elucidation of this point might be expected to vield interesting results.

seedThe

We now come to the consideration of a most characteristic organ of the seed--the pollen-chamber. This cavity arises at the apex of the megasporangium, above the big megaspore, and is found in all the Palæozoic seeds, with the sole exception, so far as I am aware, of the like " structures in Lepidocarpon and Miadesmia. utility of the pollen-chamber is manifest, but its antecedents are quite unknown. Upon such a structure as this may have depended the success of the seed-method at a critical stage in its evolution. In the viviparous Selaginellas, described some years ago in America, the archegonium on the prothallus of the retained megaspore is fertilised by sperms liberated from microspores which

become caught in the lips of the open megasporangial wall. This analogy suggests to us that the pollen-chamber cavity may be a relic or modification of the original place of dehiscence. If this conjecture be true, we have here what was once an exit-pore converted to the purposes of ingress, just as we find, in so many Thallophytes, tubes and beaks, once, as it is supposed, the orifices of zoospore discharge, now serving for the reception of male gametes.

A great feature in the early seed types was the complexity of the integument, and this still holds good in recent Cycads and some other Gymnosperms. Protective envelopes are so commonly associated with reproductiv organs, and the nutritive conditions are so favourable to their production, that a naked nucellus strikes one as anomalous. If future research confirm the supposition that the ferns which stand in possible relation to early seedplants were ex-indusiate, like the Marattiaceæ, recent and fossil, then no doubt the seed-coat is a new formation, having no true homology with, but merely homoplastic resemblance to, ordinary Fern-indusia. The only case of a naked nucellus that recalls itself is the rather mysteriou instance of Lepidocarpon in which Dr. Scott reports th not infrequent occurrence of non-integumented megasporangia with the prothallus fully developed.

The robust nature of the seed envelope, which was ofter drupaceous, is in complete harmony with the whole character of the seed if you regard the habit at its inception as a xerophilous adaptation. And such no doubt it was, an improved method whereby the plant became 'ndependent of chance water at a very critical stage in the life-history. Some of the peculiarities of fossil seed-coats, especially the ribbing of the Lagenostomas and several other genera, may be attributed to a multiple origin al this structure, at any rate in some cases. The remarkable circlet of tentacles which surrounds the summit of Lagenstoma physoides (best known by Williamson's earlier name Physostoma elegans) suggests that a number of foliar lobes have been incorporated in the seed, whilst the presence o perimicropylar ridges and the septate canopy in allied forms may be taken as only a less evident indication of the same thing.

The relation between the integument and sporangial body of recent Gymnosperm seeds is found to be an inconstant character, and the same is true of the fossils. In general character the relationship recalls that which obtains between the ovary and receptacle of an Angiosperm. The Lagenostomas resemble Cycas and Pinus in having the integument free at the apex only, whilst Taxus, Phyllocladus, and Araucaria are in agreement with the Trigonorarpons and other seeds, which are generally attributed to Medullosc in having an integument which rises freely from the chalaza. It is interesting to note that the fossil seeds o the latter group show an additional complexity in the wa!! of the nucellus. For in them a series of tracheal strandor even a mantle of tracheides is found running up from the chalaza to the pollen-chamber. It is evident that nothing was spared in these older seeds to ensure adequate access of water to the pollen-chamber where the spermmust have been liberated.

0

In due time the protective sheath, or testa, appropriate other functions supplementary to that of protection. these the most important must have been the reception of the pollen. A very striking feature in all the Lagencstomas is the way in which the tip of the nucellus (wher the orifice of the pollen-chamber is situated) projects bevond the integument. In these seeds the microspores must have had direct access to the pollen-chamber without first de scending a micropylar canal.

In the Medullosean seeds also the nucellus is dis tinguished by a long beak, as Dr. Scott and Mr. Masien have shown recently for Trigonocarpon, and, as we know in Stephanospermum, and many other cases. So far as ar know, this beak does not extend to the surface, though i engages with the micropylar canal, and is continued some distance up.

Though it can hardly be supposed that the long beak has been inherited from the ancestral sporangium, its presente may be none the less significant of what took place whe the seed method was initiated. The direct pollination in Lagenostoma may well be a survival from the old days when no proper micropyle existed. But when the micr