LECTURE VII 

 CARNIVOROUS PLANTS 



Introduction — The Bladderworts or Utricularise — Pitcher-plants, Nepenthes — The 

 Toothwort, Lathrsea — The Butterwort, Pinguicula — The Sundew, Drosera — The Flytrap 

 — Aldrovandia — Conclusions. 



That the principle of selection dominates, to a large extent at 

 least, all the structural characters of plants, and moulds these in direct 

 relation to the prospects of greater success which may be offered in 

 the vicissitudes of the life-conditions of a single species or group 

 of species, is nowhere more apparent than in the case of the so-called 

 ' insectivorous ' or ' carnivorous ' plants. Here again it was Charles 

 Darwin who led the way, for while many plants had long been 

 known on the sticky leaves of which insects were often caught 

 and killed, it had occurred to no one to regard this as of any special 

 use for the plant, much less to look on the peculiar dispositions of 

 such leaves as especially determined for this purpose. Darwin was 

 the first to show that there is no small number of plants — we now 

 know about 500 — which secure only a portion of their nutritive 

 material by the usual method of assimilation, and gain another and 

 smaller portion by dissolving and utilizing animal protoplasm, 

 especially nitrogenous muscle substance. The correctness of this 

 interpretation was at first disputed, but Darwin showed that pieces 

 of muscle, or any nitrogenous organic substance, were really dissolved 

 by the relevant parts of the plant, and were afterwards absorbed. It 

 can therefore no longer be doubted that the remarkable contrivances 

 by which animals are laid hold of by plants — are in a certain sense 

 caught and killed — have arisen with reference to this particular end; 

 or, to speak less metaphorically, that existing structural and functional 

 peculiarities in a plant which caused animals to be held fast were 

 of advantage to the nutrition of the plant, and were therefore 

 augmented and perfected by natural selection. That this was possible 

 is obvious from the number of insectivorous plants which now live 

 upon the earth, and that these processes of selection ran their courses 

 quite independently of one another, and even that they started from 

 different parts of the plant, is shown by the diversity of the con- 



