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which becomes the fruit: or, in other words, the pistil, after this impregnation, arrives at maturity, and the ovary of the pistil becomes the pericarp of the fruit. This main fact remains in all cases unaltered, though in consequence of the non-development or obliteration of some of the parts, the identity of the fruit with the original pistil is sometimes difficult to recognize. Various names have been applied to fruits according to their form, nature, &c.-All, however, are receptacles for the seed, which is the perfect state of the ovule, as the fruit generally, is of the pistil.

The provisions for ensuring this necessary contact between the pollen and the stigma, are among some of the most curious in nature. The stamens of many plants, by a spontaneous movement, approach the pistil at the season when fructification should commence. The action of water on the pollen, which would be injurious to it, is in some cases avoided by the corolla closing on the approach of rain, and in aquatic plants the organs of fructification are defended from wet, by being produced in a cavity filled with air, or by the flowers being raised above the surface of the water. The Vallisneria, whose flowers are diæceous (that is, the pistil is situated on one plant, and the stamens on another) is a very remarkable instance of the method by which the contact of the two organs is effected. It grows in the waters of the south of Europe, strongly embedded in the mud by its roots. The pistils are situated in flowers which are on long peduncles, spirally rolled up at first, but which uncurl till they reach the surface. The flowers which bear the stamens have, on the contrary, a very short peduncle, but the buds form little bladders, on which they float, detached from

their stems, around the pistilliferous flowers, they then expand, emit their pollen, and die.

68. The seed itself consists, as has been stated above (65), of an embryo, and of the albumen, &c., which nourish and protect it. This embryo," the organized body that lies within the seed, and for the purpose of protecting and nourishing which the seed was created," "consists of the cotyledons, the radicle, the plumule, and the collar."* The cotyledons are those undeveloped leaves which are seen to push their way above the ground when a plant first makes its appearance: they vary in number, but most usually there are either one or two of them. If a plant have but one cotyledon, it is said to be Monocotyledonous, which is the case with all the Endogenous tribes; if there be two or more, the plant is called Dicotyledonous, in which latter division all the Exogenous tribes are found. The Cryptogamia are all Acotyledonous-that is, without cotyledons.

69. The ascending portion of the embryo plant is called the plumule, and is sometimes hardly distinguishable from the cotyledons; the descending portion is named the radicle, and forms the future root, &c. the collar is the line of separation between them. "When the seed is called into action, germination takes place. The juices of the plant, which before were insipid, immediately afterwards abound with sugar,' as in the conversion of barley into malt, "which process consists in promoting the germination of the seed by moderate heat and moisture, and checking it by the higher temperature of the kiln as soon as the largest possible quantity of saccharine matter is formed. When the seed has germinated, and sugar is produced, the period of

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growth commences.' This growth is in the first instance caused by the absorption and decomposition of water, whose oxygen combines with the superfluous carbon of the seed, and is expelled in the form of carbonic acid gas. When the absorption of oxygen has removed a sufficient quantity of carbon from the seed, "the young plant begins to absorb food, and to grow by the processes of assimilation and respiration already described;" and as soon as the seed is once active it receives, by a special provision of nature, a larger proportional share of the sap than any other part of the plant. Probably the heat produced by the consumption of its carbon is also essential to the welfare of the newly formed plant, and may give the necessary stimulus which brings its organs into action.

70. The fact that darkness is essential to germination has long been known-"an embryo, exposed to constant light, would not germinate at all, and hence the care taken by nature to provide a covering to all embryos in the form of the integument of the seed, or of a pericarp." Mr. Hunt has recently turned his attention to this subject, and he remarks thus on it: "It is not at present in our power to explain in anything like a satisfactory manner the way in which the luminous rays act in preventing germination. The changes which take place in the seed during the process have been investigated by Saussure oxygen gas is consumed, and carbonic acid gas evolved; and the volume of the latter is exactly equal to the volume of the former. The grain weighs less after germination than it did before; the loss of weight varying from one-third to one-fifth. This loss of course depends on the combination of its carbon with the oxygen absorbed, which is evolved as carbonic acid. According to

Prout, malted and unmalted Barley differ in the fol

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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."+

"One very remarkable result," says Mr. Hunt, "must be noticed; under all ordinary circumstances plants bend in a very decided manner towards the

*Researches on Light," p. 192.

+ Ib., p. 191.

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.

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