If the reader will turn to the article KINETo; GENESIS, he will see how exactly parallel are the eases cited with those mentioned for plants by Henslow. ID part lie says: "In alluding to the above instances of levers and mechanical powers in plants, one mentally recalls how abun dant they are in the distribution of the bones and muscles in vertebrates. I cannot help thinking, therefore, that the old view was fundamentally correct ; that such have been gradually brought into existence by the efforts to meet the strain put upon them. If this be trite, then one and the same law has prevailed in the evolution of organs in both the animal and vegetable kingdoms." The accompanying figure ex plains how the forms of the ealyx and corolla are adjusted to bear the weight of the insect. The bee, he says, alights On the lip and then partly crawls into the expanded mouth of the co rolla. so that its weight now lies in the direction of 2l'. The fulcrum will be at. f, and the resultant of these is in the opposite direction to 2'. This is where the strain will lie felt ; "so that it is just at this point where the haekward curvature takes place which gives strength to the corolla-tulle. This latter is greatly supported by the tube of the calyx, which, as stated, has a curiously thickened cylin der within the mesophyl." Other structures, as projecting hairs, are so situated as to form obstructions to the entry of small insects which would be unable to pollinate the flower. In th:, gentian there are tooth-like processes at the entrance of the corolla; in the Indian pipe and a Daphne a large cireular stig ma nearly blocks up the tube. Insects have been repeatedly observed to lick the various parts of flowers, and thus maintain an intermittent irri tation and consequent formation of hairs and other products. Nutter has often watched a tly (1 hingiu rostrota) licking the stamina] hairs of a Verbaseum, and in many ease, the hairs on the filaments offer a foothold to the insects while visiting the flowers, as in the mullein; such hairs, Henslow claims, "being the actual result of the insects clutching the filaments or rubbing them with their clans."
The chief attraction of flowers to insects is of course their honey-glands or nectaries, and these are thought by llenslow to have originated from the visits of insects which, at first attracted to the juicy tissues of flowers, "by perpetually with drawing fluids have thereby kept up a flow of the secretion which has become hereditary, while the irritated spot has developed into a glandular secreting organ." These spots occur at. different places in different flowers, "wherever the pre vailing insect found it convenient to search." On the other hand, neetaries disappear, when the whole flower degenerates and becomes regularly self-fertilizing or else anemophilous, so that insects do not visit them. Henslow even suggests that the insectivorous pitchers of Nepenthes may have been due to the external irritation caused by insects, for Sir J. D. Hooker had already shown that they originate from water-glands. The continuous flow of nectar has its analogy in the daily regular, though intermit tent, mechanical irritation, and its inherited effects, which keep up the secretion of milk in the goat and cow. Ants play their part in bring ing about changes in what are called. for this reason, 'ant plants.' The hypertrophied stipules or thorns of Acacia, and the stems of eodinin. as shown by Beccari, are due to the irritation set up by these insects, which bring about a hypertrophy of the cellular tissue. A small swelling appears on the tigellum of Alyrine codium, serving the purpose of a reservoir of water, which only grows larger through the agency of ants. ITenslow also attributes the large honey-pits at the base of the leafstalks on Acacia spinerocephala. as well as the terminal `fruit bodies' occurring on the tips of the leaf lets, to the same cause—viz, the mechanical irri tation of the ants.