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 chietly of delicate hyphe, which ramify 
in the nutrient substratum, either living or dead, and which 
absorb elaborated products of some complexity freely by 
their whole surface. They have, therefore, no need of 
WES 
IS 
Fic. 146.—Thesium alpinum. Priecu or A Roor wirn 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 
