240 THE BIOLOGY OF FLOWERING PLANTS 



intimately connected the two organisms may be, is essen- 

 tially dualistic and antagonistic. 



As regards MacBougal's and Peirce's experiments, we 

 may say that they offer no indication of how even the most 

 elementary form of parasitic connection might be brought 

 about ; none of their plants, even though planted in wounds, 

 give any sign of forming an organic connection with the 

 " hosts." They are, in fact, simply plants growing in an 

 abnormal substratum and showing some sign of the fact 

 in hunger stunting. To interpret the stunting as in any 

 way analogous to the reduction seen in parasites seems 

 unnecessary. Such experiments are certainly interesting, 

 but they are only the first beginnings of experimental 

 investigation of this problem. MoUiard's cress approaches 

 parasitism rather more closely. 



§ 2. Saprophytes 



Saprophytic flowering plants are much less numerous 

 than parasites. Complete saprophytes as a rule lack 

 chlorophyll and show reduction in vegetative structure. 

 Even so typical a saprophyte as the bird's-nest orchis, 

 however, possesses a little chlorophyll masked by a brown 

 pigment ; assimilation is probably insignificant in such 

 cases. 



The saprophytes live in soils rich in humus, and most 

 characteristically in the mould of woods. Their subter- 

 ranean system consists of rhizomes or roots. In some, 

 e.g. the coral-root orchis, roots are absent, their function 

 being performed by the much-branched rhizomes. All 

 saprophytes are symbiotic with mycorhizal fungi which 

 evidently play a part in their nutrition ; the saprophytic 

 orchid Wullschlcegelia aphylla alone is said to be an ex- 

 ception to this rule (Ramsbottom, 1922). What Httle is 

 known of this in detail will be referred to in connection with 

 the general problem of mycorhiza. As we shall see, a great 

 many green plants which have no appearance of leading a 

 saprophytic existence also possess mycorhiza and grow in 



