and stamens often occurs in pelorian Pelargoniums, Horsechestnut, etc.

If pelorian forms were equally constant as the one-spurred condition, botanists would undoubtedly have recognized them as species, or perhaps genera, as it is the comparatively slight difference in the length of the spur upon which they separate Linaria from Antirrhinum. Similarly Corydalis has normally but one spur and one nectary. It, however, bears occasionally two spurs and has two nectaries, as in Dicentra.

"Peloria, then," as Dr. Masters observes,* "is especially interesting, physiologically as well as morphologically. It is also of value in a systematic point of view, as showing how closely the deviations from the ordinary form of one plant represent the ordinary conditions of another; thus the peloric 'sleeve-like' form of Calceolaria resembles the flowers of Fabiana, and De Candolle, comparing the peloric flowers of the Scrophulariaceae with those [the normal ones] of Solanaceae, concluded that the former natural order was only an habitual alteration from the type of the latter. Peloric flowers of Papilionacea in this way are undistinguishable from those of Rosacea. In like manner we may trace an analogy between the normal one-spurred Delphinium and the five-spurred Aquilegia, an analogy strengthened by such a case as that of the five-spurred flower of Delphinium."

* Teratology, p. 236.

CHAPTER XV.

THE ORIGIN OF FLORAL APPENDAGES.

EPIDERMAL TRICHOMES, ETC.--While all conspicuous flowers invite insects of some sort or another to visit them, which, by so doing, pollinate their stigmas, it is an important thing to be able to exclude those which would rifle the flower of its treasures and yet not transfer the pollen from one flower to another. Dr. Kerner, in his interesting work entitled Flowers and their Unbidden Guests, has described and figured a large number of instances of the forms of flowers in which he detects various processes, some of which produce sticky secretions, others occurring as hairy " wheels" and "tangles of wool, etc.; all of which tend to stop the ingress of ants and other small insects, and thus prevent them from getting at the honey. The question at once arises, How have these processes been caused ? Without attempting to account for all, the theory I offer will, I maintain, be answerable for a good many, especially for several cases of secretive processes and for the hairy obstructions. All these I would suggest as the immediate results of the irritations set up by insects; so that, as a consequence, they occur just and only where they are wanted; so that, while they form no hindrance to the larger and stronger insects which have presumably caused them to be developed, they, however, may effectually prevent the smaller ones from entering.

In many cases the capability of the flower to restrict itself to its proper visitors, and at the same time to exclude the wrong ones, is a common result of the differentiations which have taken place. Thus, an elongated tube, as in Evening Primrose, and in some species of Narcissus, etc., is a direct result of and adaptation to the long proboscides of Lepidoptera, and in proportion as the tube is elongated so does it prevent the ingress of short-tongued insects, or of those with short proboscides.

Apart, however, from such and other general results of adaptations, whereby flowers have become, for example, irregular, and consequently their insect visitors are more and more restricted in number, there are innumerable outgrowths of various kinds which act as special obstructions to the entry of small insects which would not be able to pollinate the flower. Thus, while many regular flowers, such as Gentians, have developed horizontal hairs all round the entrance to the tube of the corolla, Honeysuckle and Veronica Chamaedrys, which are irregular and approached from one side only, have developed them in the anterior side alone. In

Amaryllis belladonna Kerner describes and figures (Fig. 41) a one-sided flap growing out of the perianth, and so folded as to furnish a very small orifice for the entrance of a proboscis. There is no such growth on the anterior side, but only on that one, the posterior, which is probed by an insect.

In Gentiana Bavarica there are tooth-like processes at the entrance of the tube, which remind one of the appendages to the corolla of some of the Silenea. Monotropa glabra and Daphne Blagayana agree in having a large circular

stigma nearly blocking up the tube; and while in the former the irritation set up by the proboscis of an insect has (presumably) given rise to a glutinous secretion, in the latter it has caused a development of hair.*

Did we but know what the insects were, and how they have poised themselves upon the flower, and in what way their proboscides and tongues have irritated the different parts, one might be able to describe more accurately the whole process; but that such has been the cause and effect, as above described, seems to me to be too probable a theory to be hastily discarded in the absence of a better one.

It is one of those arguments of deduction that escape the opportunity of verification, and can only rest for support upon the number of coincidences which can be found, and which collectively furnish a probability of a high order.

When, then, we find that these processes always occur just where we know the heads, legs, bodies, and proboscides or tongues of insects habitually are placed and irritate the flower, we are justified in recognizing, not only a coincidence, but a cause and effect, though we may not be able to trace the action in each individual case. Thus, it may be asked,

*The remarkable fact of Heliotrope being the solitary exception out of the order Apocynaceae, with the stigma forming a circular rim below the summit, may meet with its interpretation from a like cause. The corolla is so folded round the style that it leaves no space between it and the latter. Hence it may, perhaps, have been due to a similar "rubbing," that has transferred the stigmatic surface from the now abandoned apex to a lower level, just where the style-arms ought to begin to diverge. The papillæ, too, differ from the ordinary form in being pointed like fine hairs. The relative differences in the distribution of the papillæ on the style-arms of the Composite, I would also suggest as having been brought about by different insects which irritate them in various ways. So, too, the diverging stigmas of insect-fertilised cruciferous flowers may be compared with the small globular form of self-fertilising species of the Cruciferæ.

Why are the three anterior petals of Tropeolum fringed, but the two posterior, which stand a long way behind, not so ? Why are hairs produced on the anterior side of a Honeysuckle and Veronica, but all round the mouth of the regular Gentiana? And many other questions of a like sort might be raised. If we watch the habits of insects with their tongues, we may easily see how they irritate the various parts by licking them, not solely where the honey is secreted, but the filaments, etc. Thus Müller often watched Rhingia rostrata licking the staminal hairs of Verbascum phœniceum, and in many cases the hairs on the filaments offer a foothold to the insects while visiting the flowers, as in species of Mullein; such hairs, if my theory be true, being the actual result of the insects clutching the filaments or rubbing them with their claws. In Centaurea, the epidermål cells of the filaments have produced projecting processes, just where the proboscis rubs against them when searching for honey in the little cup (see Fig. 11, p. 60), from the middle of which the style issues, as shown by the direction of the arrow.

These filaments also exhibit their extreme irritability by contracting, and so assisting in the "piston action" by dragging the anther-cylinder downwards over the style.

While recognizing the coincidence between the localization of outgrowths, enations, trichomes, etc., and the position of the parts of insects in contact with flowers when searching for honey, one must not forget that a great number occur where such contacts do not take place. Hence we must look for other possible causes for their origin as well. One of the commonest forms of trichomes is glandular hairs, and, as Dr. Kerner has pointed out, when they occur on sepals, pedicels, etc., they form admirable barriers to the approach of ants and other creeping insects, which might rifle the flower and yet not fertilise it. We must be on our guard, however, in