338 



ASSIMILATION. 



nutriment from the decaying or decayed remains of other plants ; 

 while others, like Monotropa uni flora and the Orobanchacese, 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 the}' procure all the ternary substances 

 needed for their own fabric, and also the nitrogenous substances 

 needed for their own protoplasmic matters. It is not known 

 exactly how saprophytes turn to account the comparatively inert 

 nitrogenous matters of vegetable mould, but the process is thought 

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

 somewhat similar to that which effects changes in the food within, 

 reach of the embiyo of the seed. 



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



organisms. In some cases the} T 

 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 

 chlorophyll which they possess, a 

 small part of their food. The 

 haustoria, by means of which they 

 abstract from other plants the as- 

 similated matters, have been de- 

 scribed in 351. After the parasite 

 has fairly fastened itself upon the 

 host-plant, it acts with respect to 

 the tissues of the latter much as if 

 it were an offshoot of the host. It 

 appropriates the assimilated matters 

 as they are needed, and consumes 

 them in substantially the same wa} r 

 that an embryo consumes the food stored in the endosperm. 1 



888. Insectivorous or carnivorous plants, as already explained 

 in Volume I. page 110, et seq., are those 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 Pflanzenkrankheiten, 1879. 



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

 Its host have been examined by Eeinsch. 



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

 right-hand sketches; in the other sketch, the adult plant, with its flower-clusters, at- 

 tached to the living stem of another plant. 



152 



