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flower began to fade. From the 14th to the 19th the temperature increased daily, during the night and in the morning falling back to nearly that of the surrounding air. The maximum of elevation of temperature above that of the atmosphere occurred, —

On the 14th, at 3 P.M. 4.50 centigrade

15th, 4 P.m. 10°
16th, 5 P.M. 10:20
17th, 5 P.M. 11°
18th, 11 A.M. 8.2°

19th, 10 A.M. 2.5° These maxima might be almost compared to the access of an intermittent fever.

Vrolik and Vriese consider the so called Arum cordifolium of the Isle of France to be the same as the aforesaid Colocasia odora, upon whose temperature they made very numerous hourly observations in the Botanical Garden of Amsterdam, the result of which was, that the maximum of difference observed between the temperature of the spadix and that of the green-house amounted to 10° centig. (Ann. des Sc. vol. v. 145.) Göppert adds that plants are generally warmer than the air which surrounds them. (Ueber warme Entwickelung in der lebenden Pflanze. Wien, 1832.)

That these phenomena should not be observed in ordinary cases, is no proof that they do not also occur; for it is easy to comprehend that, when flowers are freely exposed to the external air, the small amount of caloric which any one may give off will be instantly dispersed in the surrounding air, before the most delicate instrument can be sensible of it; and that it is in those instances only of large quantities of flowers collected within a hollow case, like a spathe, which prevents the heat escaping when evolved, that we can hope to measure it.

From experiments of Saussure, it seems certain that the disengagement of heat, and, consequently, destruction of oxygen, is chiefly caused by the action of the anthers, or at least of the organs of fecundation, as appears from the following table:

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It was also found that flowers in which the stamens, disk, pistil, and receptacle, only, were left, consumed more oxygen than those that had floral envelopes, as is shown by the following table:

Species.

Oxygen destroyed.
Duration
of the

By the usual organs
Experiment. By the flowers entire.]

I only.

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.

And it is here to be noticed, that those whose sexual apparatus destroyed the most oxygen have the greatest quantity of disk, and vice versa ; with the exception of Cobæa scandens, in which the disk is very firm and persistent, and probably, therefore, acts very slowly.

When the cup-shaped disk of the male flowers of the Gourd was separated from the anthers, the latter only consumed 11:7 times their volume of oxygen, in the same space of time which was sufficient for the destruction of sixteen times their volume when the disk remained. The spathe of Arum maculatum consumed, in twenty-four hours, five times its volume of oxygen; the termination of the spadix thirty times; the sexual apparatus 132 times, in the same space of time.

An entire Arum Dracunculus, in twenty-four hours, destroyed thirteen times its volume of oxygen; without its spathe fifty-seven times; cut into four pieces, its spathe destroyed half its volume of oxygen; the terminal appendix twenty-six times; the male organs 135 times; the female organs ten times.

The same ingenious observer also ascertained that double flowers, that is to say those whose petals replace sexual organs, vitiate the air much less than single flowers, in which the sexual organs are perfect.

Is it not then, concludes Dunal, probable, that the consequence of all these phenomena is the elaboration of a matter destined to the nutriment of the sexual organs ? since the production of heat and the destruction of oxygen are in direct relation to the abundance of glandular surface, and since these phenomena arrive at their maximum of intensity at the exact period when the anthers are most developed, and the sexual organs in the greatest state of activity,

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Having already, in the last chapter, explained the separate action of the stamens and pistils, I shall now confine myself to the consideration of their physical effect upon each other.

The duty of the stamens is to produce the matter called pollen, which has the power of fertilising the pistil through its stigma. The stamens are, therefore, the representatives, in plants, of the male sex, the pistil of the female sex.

The old philosophers, in tracing analogies between plants and animals, were led to attribute sexes to the former, chiefly in consequence of the practice among their countrymen of artificially fertilising the female flowers of the date with those which they considered male, and also from the existence of a similar custom with regard to figs. This opinion, however, was not accompanied by any distinct idea of the respective functions of particular organs, as is evident from their confounding causes so essentially different as fertilisation and caprification ; nor was it generally applied, although Pliny, when he said that “ all trees and herbs are furnished with both sexes,” may seem to contradict this statement; at least, he indicated no particular organ in which they resided. Nor does it appear that more distinct evidence existed of the universal sexuality of vegetables till about the year 1676, when it was for the first time clearly pointed out by Sir

Thomas Millington and Grew. Claims are, indeed, laid to a priority of discovery over the latter observer by Cæsalpinus, Malpighi, and others; but there is nothing so precise in their works as we find in the declaration of Grew, “that the attire (meaning stamens) do serve as the male for the generation of the seed.” It would not be consistent with the plan of this work, to enter into any detailed account of the gradual advances which such opinions made in the world, nor to trace the progress of discovery of the precise nature of the several parts of the stamens and pistil. Suffice it to say, that, in the hands of Linnæus, the doctrine of the sexuality of plants seemed finally established, never again to be seriously controverted; for it must be admitted, that the denial of this fact, which has been since occasionally made by such men as Alston, Smellie, and Schelver, has carried no conviction with it. We know that the powder which is contained in the case of the anthers, and which is called pollen, must come in contact with the viscid surface of the stigma, or no fecundation can take place. It is possible, indeed, without this happening, that the fruit may increase in size, and that the seminal integuments may even be greatly developed; the elements of all these parts existing before the action of the pollen can take effect : but, under such circumstances, whatever may be the developement of either the pericarp or the seeds, no embryo can be formed. This universality of sexes in vegetables must not, however, be supposed to extend further than what are usually called, chiefly from that circumstance, perfect plants. In cryptogamic plants, beginning with Ferns, and proceeding downwards to Fungi, there are either no sexual organs whatever, or they are not analogous in structure to those of flowering plants.

In order to insure the certain emission of the pollen at the precise period when it is required, a beautiful contrivance has been prepared. Purkinge has demonstrated the correctness of Mirbel's opinion in 1808, that the cause of the dehiscence of the anther is its lining, consisting of cellular tissue, cut into slits, and eminently hygrometrical. He shows that this lining is composed of cellular tissue, chiefly of the fibrous kind, which forms an infinite multitude of little springs, that, when dry, contract and pull back the valves of the anthers, by a powerful accumulation of forces, individually scarcely appreciable: so that the opening of the anther is not a mere act of chance, but the admirably contrived result of the maturity of the pollen; an epoch at which the surrounding tissue is necessarily exhausted of its fluid, by the force of endosmose exercised by each particular grain of pollen.

That this exhaustion of the circumambient tissue by the

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