48 



PHYSIOLOGY OF NUTRITION 



Almost the only definitely known fact concerning the nutrition of seed- 

 plants without chlorophyll is that some are saprophytes and others parasites. 

 The former utilize decomposition products from plants and animals, while the 

 latter attach themselves to living plants and derive nourishment therefrom. 



The widely distributed dodder (species of Cuscuta) is an example of a para- 

 site. It is parasitic upon nettles, hops and many other plants (Fig. 28). 

 Parasitism exhibits such a high state of development in some flowering 

 plants without chlorophyll that they possess neither root not stem, nor have 

 they any leaves. The entire plant body here resembles a fungus in its struc- 

 ture, consisting of branching filaments each composed of a row of cells, very 

 similar to fungus hyphae. The Balanophoreae, Hydnorese and Rafflesiacese, 

 are examples of such plants. The hypha-like body of these plants develops 

 within various trees and derives nourishment therefrom after the manner of 



Fig. 28. — Section of stem of Cuscuta europaa, attached, by means of its haustorium, to the 

 stem of a nettle. E represents the epidermis of the nettle. 



many fungi. The flower buds and flowers of these non-green parasites appear 

 upon the branches of the host only during the flowering season of the latter. 

 It then appears, at first glance, as though the plant infested by the parasite were 

 bearing two kinds of flowers. In reality, however, some of these are the true 

 flowers of the host plant, while the others belong to the parasite. Fig. 29 shows 

 a portion of an underground stem of a host plant, bearing its own flower buds 

 and a mature flower of a parasite, Hydnora africana. 



§3. Assimilation of Energy from Inorganic Substances by Plants without 

 Chlorophyll. — Some bacteria are so constituted as to be able to obtain their 

 energy from oxidizable inorganic substances that are common on the earth. 

 Of these the nitrifying bacteria, which oxidize ammonia into nitric acid, are the 

 most important. The absence of organic substances is necessary for their 

 successful growth. Vinogradskii succeeded in obtaining a pure culture of 



