INFLUENCE OF ENVIRONMENT ON PLANTS 349 



but they lack a great deal of the constructive power of the 

 latter. 



The degradation of the structure of such plants is 

 associated with the absence of the constructive processes 

 which depend on the presence of chlorophyll. Their body 

 is usually composed chiefly of delicate hyphae, which ramify 

 in the nutrient substratum, either living ur dead, and which 

 absorb elaborated products of some complexity freely by 

 their whole surface. They have, therefore, no need of 



FIG. 146. Thesium alpinum. PIECE OF A ROOT WITH SUCKER 

 IN SECTION, x 35. (After Kerner.) 



differentiated absorbing or conducting tissues, and these are 

 consequently not developed. A further consequence of the 

 ease with which they obtain their food is the readiness with 

 which vegetative and asexual reproduction is brought about ; 

 hence sexuality is in many cases non-existent among them. 

 Phanerogams which are completely parasitic show a 

 similar degradation of structure. They possess no chloro- 

 plasts, their leaves are absent or reduced to the condition 

 of scales, while their stems are often thick and succulent. 

 Their roots are replaced by the so-called haustoria, which 



