ON THE STUDY OF ADAPTATION IN PLANTS. 1S1 



frequently cautious and critical treatment in these questions 

 may fail. 



In physical adaptations the conditions of life in plants 

 have not been sufficiently taken into consideration. It has 

 been concluded, for instance, that, because the leaves of a 

 plant show certain structural arrangements which involve 

 the reducing of transpiration, they must on that account 

 grow in dry situations. In many cases this is true, but in 

 others not. For we meet with exactlv the same structural 

 peculiarities in plants which are found in wet and swampy 

 regions ; the absorption of the water is rendered difficult, 

 either on account of ihe saline properties of the liquid, or 

 the low temperature of the soil. 1 We have some very 

 striking: instances of the last fact amono- our native marsh- 

 plants ; the habitus of a [uncus, for example, is distinctly 

 Xerophilous. Among the so-called irritable plants the 

 Mimosa is one of the most striking. It has been conjec- 

 tured that its movements form a protection against the 

 injuries caused by hail. But in the regions where Mimosa 

 grows, it either does not hail at all, or only quite exception- 

 ally. The tendency to sleep on the part of the leaves has 

 been pointed out as a protection against the radiation of 

 heat. But very many tropical plants exhibit this tendency 

 to sleep, and in those parts of the world there can scarcely 

 be a question of the need of protection in this respect. 



Insectivorae have recently occupied a considerable share 

 of attention,' 2 not only from a morphological but also from 

 a physiological point of view. As regards the latter I will 

 only mention the fact that Sarracenia and Cepkalotus do 

 not possess a digesting ferment or enzyme, but the Cepka- 

 lotus secretes into its pitcher a substance which works 

 antiseptically. It was also recently maintained — in contra- 

 diction to the statements of Hooker, Darwin, Rees, Vines 

 and others — that in the case of Drosera, Nepenthes and 

 Pinguicula no actual digestion obtains, but that the solution 



1 For striking instances of this, cf. Pflanzenbiol. Schilderungen, ii., 



P- 3- 



2 Pflanzenbiol. Schilderungen, ii. theil. 



