33J 



ASSIMILATION. 



nutriment fi'om the decaj-ing or decayed remains of other plants ; 

 while others, like Monotiopa uniflora and the Orobanchaceae, ob- 

 tain part of their food from living plants. True parasites obtain 

 their nourishment from living organisms, whereas humus-plants, 

 or saprophytes, live upon the structures of dead ones. From the 

 decaying vegetable mould thej' procure all the ternar3' substances 

 needed for their own fabric, and also the nitrogenous substances 

 needed for tlieir own protoplasmic matters. It is not known 

 exactly how saprophjtes turn to account the comparatively inert 

 nitrogenous matters of vegetable mould, but the pi'ocess is thought 

 to depend upon the action of a solvent, unorganized ferment, 

 somewhat similar to that which effects changes in ths food within 

 reach of the embr3o of the seed. 



887. Parasites obtain a large part of their food from living 



organisms. In some cases they 

 appear to be able thus to procure 

 all the food they require ; but most 

 of them can be shown to elaborate, 

 by means of the small amount of 

 chlorophj-U which they possess, a 

 small part of their food. The 

 haustoria, by means of which they 

 abstract from other plants the as- 

 similated matters, liave been de- 

 scribed in 351. After the parasite 

 has fairlj' fastened itself upon the 

 host-plant, it acts with respect to 

 the tissues of tlie latter much as if 

 it were an offshoot of the host. It 

 appropriates the assimilated matters 

 as they ai-e needed, and consumes 

 them in substantially the same way 



that an embr^-o consumes the food stored in the endosperm.^ 



888. Insectivorous or carnivorous plants, as already explained 

 in Volume I. page 110, et seq., are tiiose which are provided with 

 some specialized apparatus for the utilization of animal matters. 



1 For an interesting account of the more striking effects produced upon the 

 host-plant, the reader should consult Frank ; Die PHanzenkrankheiten, 1879. 



The relations which exist between the ash-constitueuts of the parasite and 

 Its host have been examined by Reinsch. 



Fio. 152. Cuscuta, a parasite. The coiled embryo and seedling are shown in the 

 Tight-band sketches ; in the other sketch, the adult plant, with its fluwer-clusters, at- 

 tached to the living stem of another plant. 



