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Prout, malted and unmalted Barley differ in the following respects:
Resin . . . . I 1
This shows that the insoluble principle, hordein, is, in the process of germination, converted into the soluble and nutritive principles, starch, gum, and sugar. We are therefore at present left in considerable doubt; we can only suppose that the luminous solar rays act, as indeed we find them to do on many of the argentine preparations, in preventing those chemical changes which depend upon the absorption of oxygen. A like interference has been observed by Sir John Herschell to be exerted by the red rays of the spectrum; and from the manner in which germination is impeded in the seeds covered by deep red media, we may trace a somewhat similar influence.” All Mr. Hunt's experiments prove “that the process of germination is obstructed by the influence of light on the surface of the soil, although the bulbs and seed have been buried some depth beneath it.”f “One very remarkable result,” says Mr. Hunt, “must be noticed; under all ordinary circumstances plants bend in a very decided manner towards the
light. In all my experiments with red fluid media, they have as decidedly bent from it.”
* “Researches on Light,” p. 319.
A very curious phenomena which from its usually taking place in the evening has been called the sleep of plants, appears to be principally owing to the influence of light. The fact itself is, that in certain plants the leaves fold up, and sometimes grasp the stem. . It occurs also in some flowers which shut up periodically, and the inference that light is probably the agent in producing this effect, was drawn by M. de Candolle from the circumstance that he found the period of its occurrence could be reversed by excluding the light from the plants during the day time, and placing them in strong lamp light at night. (De Candolle, Phys. Veg., vol. ii. p. 860.)
It was remarked in an earlier part of this little work, that the influence which the study of one science has on many others, with which it appeared in the first instance to promise no connection, was illustrated by the benefit that agriculture derives from chemistry; another proof of the fact that in the observation of natural phenomena, and the rational investigation of their causes, it is impossible to foresee or limit the beneficial results which may follow, even where we have least reason to anticipate them, is afforded by the comparatively novel subject of Photography. This, which at first appeared but an ingenious application of a natural agency to the purposes of art, is assuming, in the hands of some of our greatest philosophers, the rank of a science, which promises to lead to discoveries equally curious and important. The true nature of that sunbeam, whose wonderful operation can either call forth the vital energy of a plant, cause it to perform its functions of growth and nutrition, yet prove detrimental to its germination; or delineate its portrait with a fidelity and beauty unknown to the pencil of man on the sensitive surface presented to it, has yet to be fully ascertained ; but that it has other properties than were supposed before the subject of Actino-Chemistry came under the investigation of Herschell and others, seems already established ; and who shall assign a limit to the possible results which may arise from a clearer knowledge of the nature and operation of such an agent in the universe. It may as yet seem to bear little on the immediate subject of the present work, but it is impossible to assert, that a further insight into the nature of a cause whose effects on vegetation are so decided, may not prove of great practical benefit; and although its study is no new branch of science in itself, yet the new aspect under which it is now pursued may probably lead to unanticipated Truth.
71. In whatever manner a seed may be placed in the ground, it invariably shoots forth its plumule in an ascending, and its radicle in a descending direction. Invert it as we may, the result will be the same ; but on what vital energy within the plant the constancy of this fact depends, seems yet entirely uncertain. Whether it arise from the tendency of upper portions of plants to seek the light, or from any other cause, the reason is equally obscure, and we can hardly reckon on its being ascertained by the most minute investigation; it seems to belong to that class of phenomena in nature whose ultimate principles are too subtle for our grasp, and appear to depend on that vitality which we can indeed perceive most palpably in its effects, but whose cause is known only to the Creator; whether modern science will be permitted to approximate nearer to the truth on this and some few similar subjects must remain at least doubtful: at all events we are not now in possession of any wholly satisfactory solution of the difficulty.
“That gravity is an important agent in determining the difference between the directions taken by the root and stem, is shown by an ingenious experiment of Mr. Knight. He placed some French beans on the circumference of two wheels, and so secured them that they could not be thrown off when a rapid rotatory motion was given to the wheels. One wheel was disposed horizontally, the other vertically, and both were kept in constant motion while the beans were germinating. The radicles of those beans which germinated on the vertical wheel extended themselves outwards, or from the centre, and the plumules inwards, or towards it. Those which were placed on the horizontal wheel pushed their radicles downwards and their plumules upwards; but the former were also inclined from and the latter towards the axis of the wheel. This inclination was found to be greater as the velocity of the wheel was increased. Now in the vertical wheel the effects of gravity were nullified; since the beans were constantly changing their position with respect to those parts which were alternately uppermost and lowermost, in each revolution. The only cause which could have produced the effects described must be the centrifugal force, which has here replaced the effects of gravity, compelling the root to grow outwards and the stem inwards, instead of downwards and upwards. The effect produced upon the horizontal wheel is evidently the result of the combined action of the forces—gravity inclining the root downwards, and the centrifugal force propelling it outwards; and the reverse with regard to the stem. Although it is plain that gravity is the efficient cause in establishing the directions of the stems and roots of plants, it is not so easy to understand the manner in which it produces opposite effects on these two organs. Various theories have been formed to account for this, and the most plausible is that which ascribes it to the different manners in which the newly developed tissues are added to the root and stem. In the root the addition is almost entirely confined to the very extremity, while the stem continues to increase for some time through its whole length. Hence it is supposed that the soft materials continually deposited at the extremity of the root must ever be tending downwards from the effect of gravity alone.” (Henslow's Principles of Botany, p. 292.) Is it not probable that we may find the agency of light connected with the fact of the plumule ascend72. The reproduction of the tribes of the Cryptogamia takes place in a very different manner from that of the flowering plants. In all of them it occurs spontaneously, and without any contact between one part of the plant and another. At the season of the year when the lowest tribes of all, such as the Red Snow, the Confervae, &c., are to reproduce their species, a number of small granules are liberated by the bursting asunder of the cell which enclosed them. They gradually develop themselves into cells, acquire the size and form of the parent plant, and become distinct individuals, capable in their turn of producing others like themselves. The apparatus of reproduction if we may so call it, increases in complexity as it approaches the higher orders, but in all except the cells just mentioned, the immediate organ is called a spore,” and is analogous to the seed . of the flowering plant.
73. It has been seen that in reproduction by seed, each germ has the power of becoming developed, after fecundation, into a separate individual plant, entirely distinct from that which gave it birth. In addition to this accustomed mode of increase, plants are also propagated by division; and this is either natural or artificial, and depends on two circumstances: in one, the ascending organs are first developed, or in other words an adventitious leaf bud (35) is produced, and these favor the subsequent development of the roots: in the other, roots are first formed, and by their action promote the development of the
* “It is in the spores that the power of increase resides; every one of them will form a new plant, and consequently they are analogous to seeds, but, as they do not result from the action of pollen upon a stigma, they are not real seeds, but only the representations of those organs amongst the flowerless plants.” (Lindley’s Ladies' Bot., p. 270.)