158 CARNIVOROUS PLANTS WITH ADHESIVE APPARATUS. 



aliment from prey were injurious to Dioncea, the plant would certainly have died 

 out long ago. If, therefore, cultivated specimens of Dioncea have suffered from 

 being fed with meat, fibrin, cheese, and other such materials, only this much is 

 proved, that the nutriment in question was not beneficial to them owing to its 

 quality or to its being too concentrated. 



As regards the other point, that Dioncea thrives well under cultivation, even 

 when all visits from insects are excluded, we must, on the other hand, bear in mind 

 that the successful growth of Dioncea, like that of Drosera, Pinguicula, &c., is not 

 conceivable unless in some way or another the nitrogen indispensable for the 

 construction of the protoplasm is conveyed to the individuals in question. The 

 source from which it is taken varies accordinsr to the site. If the roots are buried 

 in deep sods of bog-moss upon a flat expanse of moorland, the supply of nitrogen 

 from the ground, and also from the air, will be extremely limited, and probably 

 insufficient; under these circumstances the nutriment derived from the dead bodies 

 of captured insects would be not only useful and beneficial, but may be even 

 essential. If, on the contrary, the place where the plants have been reared or have 

 grown up spontaneously is such that they can obtain the requisite nitrogen from 

 the ground or air, they are able without harm to dispense with the available source 

 of nitrogen afforded by the capture of insects. It is worthy of notice that insect- 

 ivorous plants always grow wild only in places that are poorly supplied with nitro- 

 genous food. The majority occur in pools fed by subterranean water, whose course 

 lies through layers of peat, or in the spongy peat itself, or in the sods of Sphagnum. 

 Others are rooted in deep chinks in the stone on the declivities of rocky mountains, 

 whilst yet others occur in the sand of steppes. The water available in such situa- 

 tions for absorption by the suction-cells is, to say the least, very poorly furnished 

 with nitrogenous compounds; and the quantity of these compounds passing from 

 the ground into the air at the places mentioned is extremely minute and inconstant. 

 Under these circumstances, the acquirement of nitrogen from the albuminoid 

 compounds of dead animals is certainly of benefit, and all the various pitfalls, 

 traps, and limed twigs are explained as contrivances by means of which this 

 advantage is secured. 



