OTHER METHODS OF OBTAINING FOOD 191 
other, in some cases a very complete union of their tissues 
being effected, so that transport of elaborated food materials 
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 proteins 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 can grow 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, Botrychiwm 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 function- 
less. 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 
