SAPROPHYTES 125 
mycorhiza, associated with their roots. The saprophyte 
at first made use of it merely to obtain water, but in the 
course of time it increased its demands, and at last came 
to rely upon it for all its food. Since light is unnecessary, 
saprophytes can escape competition by living in the 
densest shade of forests, where a green plant could not exist. 
(ii.) Partial Saprophytes.—Many 
green plants also possess a mycor- 
hiza, and indirectly, therefore, live 
on humus. This is the case with 
many of our forest-trees, which in- 
habit a soil rich in a somewhat acid 
humus—e.g., pine—and with plants 
living in peat—e.g., heath. The 
mycorhiza is at first external on 
the roots and functions merely as 
root-hairs, but in those cases where 
it penetrates deeply in the tissues, 
its value to its partner increases, 
and it passes on to it something 
more than water; in fact, condi- 
tions are being established which, 
in the course of time, may lead to 
the degeneration of the green plant 
into a colourless saprophyte. 
(6) Parasites (Gr. parasites, one 
who sups at another’s table).— 
These obtain the materials for their 
nutrition—carbohydrate and _ pro- 
tein—from living hosts, animals or Fis. 40. — Corallorhiza 
innata (Corau - Roor 
plants. Among the lower plants ORcHID). 
many fungi are parasitic, and some LoD Ls tan Gi an 
that are saprophytic are capable ““inderground stem, and 
of becoming so, if circumstances absence of roots. 
allow. Swarms of bacteria are 
parasites, and though some are harmless, or even 
beneficent, others are malignant and give rise to disease. 
These lower plants are usually internal parasites, in- 
habiting the tissues of animals or plants. Higher 
plants which are parasitic attach themselves extern- 
ally to the bodies of other plants, and by means of 
special sucking organs — haustoria — penetrating the 
tissues, absorb nutriment from them. The depend- 
