spadixes stood at 111°, and in the centre of twelve, at 121o, although the temperature of the external air was only 66°. The greatest degree of heat in these experiments was at sunrise. The same observer found that the male parts of six spadixes, deprived of their glandular part, raised the temperature only to 105°; and that the same number of female spadixes only to 86°; and, finally, that the heat was wholly destroyed by preventing the spadix from coming in contact with the air.

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:

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:

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 inale 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 spatha 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 spatha fifty-seven times; cut into four pieces, its spatha 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 M. 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.

M. De Candolle has remarked, that the colouring matter of the corolla is probably very different from that of the leaves, since it will not etiolate by the exclusion of light. It may, however, be doubted whether this is strictly correct; for it is well known that forced flowers have little colour without full exposure to light, and that the intensity of colour in blossoms produced in stoves in winter is far less than that of the same species flowering in the open air in summer.

CHAPTER VII.

OF THE STAMENS AND PISTILLUM.

HAVING already, in the last chapter, explained the chemical action of the stamens and pistilla, 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 pistillum through its stigma. The stamens are therefore the representatives in plants of the male sex, the pistillum of the female sex.

The old philosophers, in tracing analogies between plants and animals, were led to attribute to the former distinction of sexes, 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; 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; the fact is, that his was rather an empirical notion than an opinion depending upon philosophical deduction. Nor does it appear that any more distinct evidence existed of the universal sexuality of vegetables till about the year 1676, when it was for the first time distinctly pointed out by Grew. Claims are, indeed, laid to a priority of discovery over this great 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 useful, if I had the space, to enter into any detailed account of the gradual advances which these opinions made in the world, nor to trace the progress of discovery of the precise nature of the several parts of the stamens and pistillum. Suffice it to say that, in the hands of Linnæus, the

doctrine of the sexuality of plants was finally established, never again to be seriously controverted; for the denial of this fact, which has been since occasionally made by a few men, such as Alston, Smellie, and Schelver, has merely exposed the weakness of such hypercritics. We know that the powder which is contained in the case of the anthers, and which is called pollen, must generally 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 pericarpium or the seeds, no embryo can be formed. I have said that it is generally indispensable that the pollen and the stigma should come in contact. To this, however, there is a notable exception in Orchideous plants, in which nature seems to have specially guarded against the pollen coming in contact with the stigma by locking it up in cells from which it is not readily disengaged; and to have provided, in the form of glands and other apparatus of the stigma, peculiar means of conveying the impregnating matter to the stigma without actual contact between the latter and the pollen. Mr. Brown has, indeed, attempted to show that even in these plants actual contact between the two parts is necessary, as, indeed, Monsieur Adolphe Brongniart had done before him; but the evidence to the contrary is so strong that we pause for proof before we admit the conjectures and statements that have been brought forward upon this subject. Another order, that of Asclepiadeæ, has also been included in the number of those in which fertilisation takes place through peculiar glands, without actual contact between stigma and pollen; but Mr. Brown states, that in this tribe the grains of pollen are enclosed in a kind of sac, the most prominent part of the convex edge of which is applied to the stigma when fecundation is about to occur; and then a number of extremely slender threads, each of which is the pollen tube of a single grain, are emitted from this edge into the tissue of the stigma: almost every grain in the sac is said to produce its

tube, and the tubes to be directed from all parts of it towards the point of dehiscence.

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 the males are so imperfectly developed as to be invisible or of no effect.

The exact mode in which the pollen took effect was for a long time an inscrutable mystery, and is even now not fully explained. It was generally supposed, that, by some subtle process, a material vivifying substance was conducted into the ovula through the style; but nothing certain was known upon the subject until the observations of Amici and of Adolphe Brongniart had been published. It is now known, that a short time after the application of the pollen to the stigma each grain of the former emits a tube of extreme tenuity, not exceeding the 1500dth or 2000dth of an inch in diameter, which pierces the conducting tissue of the stigma, and finds its way down to the region of the placenta, including within it the active molecules found in the grain; no one has actually seen the tubes pass further than the placenta; but there appears to be good reason for supposing that the vivifying matter communicated by the pollen tubes to the placenta is by some unknown means transmitted by the latter to the foramen of the ovulum, through which it finally passes into the nucleus, there to become the new embryo. In order to facilitate the contact between the placenta and the foramen of the ovulum, some very curious contrivances have been remarked. In Euphorbia Lathyris the apex of the nucleus is protruded far beyond the foramen, so as to lie within a kind of hood-like expansion of the placenta in all campulitropous ovula the foramen is bent downwards, by the unequal growth of the two sides, so as to come in contact with the conducting tissue; and in Statice Armeria, Daphne Laureola, and some other plants, the surface of the conducting tissue actually elongates and stops up the mouth of the ovulum, while impregnation is taking effect. Again, in Helianthemum and Cistus, which,