SECT AGENCY. Having seen that insects have been highly modified in various ways by the use and disuse of organs. while seeking pollen and nectar, we may now inquire into the result of such visits or stimuli upon the flowers them sel•es. Many facts and ingenious suggestions have been made by Henslow in his Origin of Floral Structures. llis conclusion is that a flower with a conspicuous corolla or perianth has originated from "a leaf-bud of which some of the members have already differentiated into carpel lary, others into staminal organs. the outer ap pendages being simply bracts, like, we will say. those surrounding the stamens or ovule of the yew." Insects probably visited the primitive flowers for pollen. hut also pierced the juicy tis sues for moistening the honey. Gradually the nectar was evolved, and after a time the earliest formed flowers having attracted insects to come to them regularly, a numerous series of differen tiations would result. The corolla, in all probabil ity, would he the first to issue out of the tracts. Other changes would follow by degrees and in different combinations. From regular. irregular flowers like those of the pea would arise. But all such changes "would be due to the responsi ye action of the protoplasm, in consequence of the irritation: set up by the weight., pressules. thrusts, tensions, (ay., of the hist-et visitors. Thus, then, do I believe that the whole floral world has arisen.• Irregular flowers, as that of the pea, have Made such by the visits of the bees rind other external influences. ll'hist a flower is situsted laterally and projects horizontally, or nearly so, an insect is compelled to alight upon it on one side only, when approaehing it directly from the front. It then throws all its weight upon the organs on the lower or anterior side of the flower, as is the case with the keel-petals of papiliona mous flower:4, with the lips of labiat•e, etc.; or else its weight is sustained by the stamens or style, or hy both together, as hi Epilobinin angustifolium, cirmea, Veronica, larkspur, and monkshood; and whenever the stamens are deelinate. as in horse chestnut. Di•tamnus, &Ilium. Amaryllis, etc. lIenslo• assumes that the primary cause of irreini larity must mane from without, from au insect —i.e. from the mechanical influence of its weight and pressures. "To this external irritation the protoplasm of the cells responds. and gives rise to tissues which are thrown out to withstand the strains due to the extraneous pressures of the in sect, and so the flower prepares itself to main tain an equilibrium under the tensions imposed upon it. and irregularities,are the result." Such
modilbeitions occur in the bilobed calyxes of furze and Salvia, with many forms of lips, and in en larged anterior petals or in dependent stamens, as those of aconite and Epilobium. The lip of Lamitnn consists of one much enlarged petal, which forms an excellent landing-place for a bee to rest upon, while the two lateral petals. not being required, arc atrophied to mere points. In like milliner, the two posterior petals are en larged to form the hood, presumably due to the backward thrust of the insect's head." Ill the irregular flowers of the foxglove and the Gloxinia, as well as Petunia to a slight extent. and in the regular campanulate flowers, the tube of the gamopetalous corolla "has enlarged so as to per mit the ingress of an insect which partly or en tirely crawls into it: then it is this tubular part which, more especially having to bear the strain upon it, bulges outward or becomes or less inflated in form, while the lip or anterior petal, not having to bear the entire burden. is not par ticularly enlarged, if it be at all." Henslow states that if no more than the head of an insect enter the flower, "then the corolla shapes itself to fit it": thus the snowberry. Serophularia. and Epipaetis only admit the heads of wasps, which are the regular visitors of these flowers. Bow, the deep tubular corolla of the evening primrose or the honeysuckle has been brought about is ex plained by the fact that butterflies. in probing their depths while on the wing, irritate the tube only. "which thus elongates and contracts. re sulting in little or no irregularity in the flowers." Also flowers like the narcissus and evening prim rose prevent the ingress of shortstonsmed insects. The origin of irregular flowers is illustrated by Davernoin adhatodoides, whose curiously shaped lip affords an excellent landing-place for a big bumblebee: "moreover. the two walls slope off. and are gripped by the legs of the bee. so that it evidently can seeure an excellent pureliase, and thus rifle the flower of its treasure at its ease." The immediate cause of the shape of the wing petals of many papilionaceous flowers is at tributed to the "weight of the insect in front, the local irritations behind, due to the thrust of the insect's head in probing for nectar, coupled with the absence of all strains upon the sides." Good examples of the occurrence of great thick ening of the tissue just where the strain will be most felt are to he seen in the slipper-shaped flowers Cypripedium. Calceolaria. etc.