The origin of floral structures through insect and other agencies . rts of the whorls are free. Thus inThalamifone, of such an order as Ranunculacea; with regularflowers and with all the parts of the perianth whorls free, theflowers are usually visited by a much greater number andvariety of insects than are those of orders of Corolliflorce. Forexample, Miiller records sixty-two species of insects as seen byhim to visit Ranunculus acris ; whereas the humble-bee aloneenters the gamopetalous tube of the Foxglove. This adapta-tion oi form to insect visitors will be better appreciated whenwe come t
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The origin of floral structures through insect and other agencies . rts of the whorls are free. Thus inThalamifone, of such an order as Ranunculacea; with regularflowers and with all the parts of the perianth whorls free, theflowers are usually visited by a much greater number andvariety of insects than are those of orders of Corolliflorce. Forexample, Miiller records sixty-two species of insects as seen byhim to visit Ranunculus acris ; whereas the humble-bee aloneenters the gamopetalous tube of the Foxglove. This adapta-tion oi form to insect visitors will be better appreciated whenwe come to discuss that principle of Variation, which sopowerfully affects floral structure. It occasionally happens that parts normally united becomefree : the process is called dialysis, and may be regardedas a reversion to an ancestral free condition. Fig. 10 repre-sents a flower of Mimulus in this condition. The rationaleof cohesion in the sepals, petals, and stamens, I regaid as theimmediate result of hypertrophy set up by insect agency, THE PRINCIPLE OF COHESION, 51. Fig. 10.—3fimulus undergoing Dialysis(after Baillon). aided by the close proximity of the parts; and. as a resulting effect, is the ever-increasing adaptation to the requirements of insects, which are more and more specialized, for them, so that, for example, Lepidoptera are almost solely adapted to long tubular flowers like the Honeysuckle. An analogous process ofcongenital cohesion is well seenin the fasciation of stems whichoccurs particularly often insucculent shoots, as Asparagus, Cabbage, Lettuce, and theyoung shoots of the Ash tree. This is most reasonablyreferred to hypertrophy coupled with the close proximityof the buds which ought to have developed into independentshoots. Again, cohesion between the sepals or petals ofOrchids is not uncommon abnormally under cultivation; andwould also seem to be due to the stimulating conditions underwhich they are artificially cultivated. Hypertrophy in an organ is due to