COMRADES OF THE PLANT WORLD 
ter which contains elaborated food material. 
Many choose the latter course, but a“ goodly 
number, especially those of primitive struc- 
ture, have entered into profitable partnerships. 
The minute one-celled plants called Zoo- 
chlorella or Zooxanthella have chosen the fresh 
water sponge Ephydatia Fluviatilis for their 
messmates. Sometimes they live with the Hy- 
dra called Viridis and impart to it a bright 
green colour. 
There are whole regiments of microscopic 
parasites which thrive on living plant tissue 
and cause spots and rust to appear on Apples, 
Peaches, Pears and other fruits and number 
among their cohorts Rose-blight, Wheat-rust, 
and various Mildews. ‘The larger messmate 
does not receive very much benefit from the re- 
lation, in this instance, except when the minute 
guests serve to cover a cut or an abrasion with 
a protective mantle, just as Mildew shields 
cheese or jelly from decay. 
Cases where Fungi render very valuable ser- 
vices to larger plants are exemplified by the 
Monotropa or Indian Pipe. This pallid scaven- 
ger grows on the decaying vegetable matter 
[61] 
