198 VEGETABLE PHYSIOLOGY 



can readily take place between them. In those cases in 

 which this close association is of benefit to both the 

 organisms it is spoken of as symbiosis ; in those in which 

 one flourishes at the expense of the other, the relationship 

 is called parasitism. While there are many cases which 

 can be definitely referred to both these categories, they 

 seem to blend one into the other, cases being known in 

 which it is very difficult or impossible to say whether the 

 advantages are all on one side or not. 



The plants which differ least from the normal habit 

 which we have described are those which are known as 

 Saprophytes, their characteristic feature being that they 

 derive at least part of their food from decaying animal or 

 vegetable matter, absorbing it in some cases as actual food- 

 stuffs, and in others as organic compounds which require 

 relatively little expenditure of energy to build them up 

 again into proteids or carbohydrates. 



Numerically the fungi are the most prominent in this 

 group, but the green plants also afford many instances of 

 the habit. Among the mosses Splachnum grows upon 

 lumps of dung, and various species of Hypnum flourish in 

 water which contains various compounds derived from the 

 decomposition of once living matter. Among higher 

 plants still, the soil of woods and pastures affords many 

 examples of individuals which depend partly upon the humus 

 of the soil and partly on their own chlorophyll. Among 

 the ferns we have notably the moon-wort, Botrychium 

 Lunaria, and among the club-mosses some species of 

 Lycopodium, while numerous flowering plants show this 

 peculiarity. 



The chlorophyll apparatus is found in nearly all of 

 them, though in some cases it is so reduced as to be 

 almost functionless. Some of our native Orchids are 

 remarkable in this respect, that they are almost, if not 

 altogether, dependent upon their saprophytism. Neottia, 

 the so-called bird's-nest orchis, has a flowering stem above 

 ground, on which are only a few rudimentary leaves. At 



