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THE PRESIDENT'S ADDRESS. 

 SOME CASES OF ADAPTATION AMONG PLANTS. 



By a. B. Rendle, M.A., D.Sc, F.R.S. 



{Delivered February Wih, 1919.) 



One of the most obvious cliaracteristics of plants is the remark- 

 able adaptation which they show to their environment. It is 

 scarcely necessary to recall instances, but I may remind you 

 that though these adaptations are sometimes so striking as to 

 impress the layman, as, for instance, in the insectivorous plants 

 which formed the subject of an address at our last meeting, 

 yet the botanist is aware that every plant, one might almost 

 say every plant-organ, represents a finely adjusted correlation 

 with its surroundings ; otherwise it would cease to exist. But 

 again it must be obvious that other factors than present environ- 

 ment govern the form and structure of plants, otherwise all the 

 plants growing in one and the same locality would show the 

 same type of adaptation. On the contrary, different species of 

 plants show widely difiering responses to the stimulus of the same 

 environment. Closely allied species growing close together may 

 show strildng differences, to the observing eye, in external form. 

 A familiar example is found in the two buttercups which you may 

 find in the same meadow, the one. Ranunculus acris, with straight 

 rootstock and spreading sepals, the other, R. hulbosus, with stem 

 swollen at the base and reflexed sepals. Here are two closely 

 allied species which, on any theory of evolution, have sprung 

 from the same ancestral form at no very distant period, and are 

 now growing side by side. The explanation of these differences 

 must be sought in the history of the two species since their 

 separation from the parent stock. But I do not propose to 

 deal with theories of evolution or the part which adaptation to 

 environment may have played in that connection. I wish merely 

 to refer to some cases which indicate what we may term the 



