60 PARASITES AND SAPROPHYTES [CHAP. 



are distributed over many orders of flowering 

 plants as well as genera of fungi. In the division 

 Thalamiflorce of Dicotyledons there is only one ; 

 in G-amopetalce, several ; in Incomplete?, five ; 

 while in Monocotyledons there are four. 



The same argument applies to fungi. There 

 are many species which attack plants, being 

 peculiar to their "hosts," respectively. Was it 

 more probable that the fitness say of JEcidium 

 Berberidis arose from an innate adaptiveness 

 to that bush, while the spore itself was being 

 formed from the " teleuto-spore " of the mildew 

 of wheat ? or did it acquire its parasitic adapta- 

 tion by direct contact with a leaf of the barberry ? 

 Induction supports the latter. 



The most obvious feature, in a large pro- 

 portion at least, is the total absence of any 

 green colouring matter or chlorophyll. All such 

 are, therefore, incapable of assimilating purely 

 inorganic food materials, and must depend wholly 

 upon living plants as hosts, or decayed organic 

 matter in the soil. 



Since it is presumable, on the score of 

 structural affinity, that greenless parasites and 

 saprophytes have descended from green plants, 

 it is not surprising to find that many such are 

 parasitic, although they can derive nourishment 

 to some limited extent by their ordinary roots 

 and leaves. As an example, species of winter 

 green (Pyrola), among the heath family, supply 



