SAPROPHYTISM AND SYMBIOSIS 325 
and independence, or of interdependence. One plant 
may merely live upon another, without deriving any 
nourishment from it (epiphytism] \ or two plants may 
be mutually helpful, each contributing something of 
advantage to the other (mutualism}', one plant may 
live at the expense of the other, deriving nourishment 
from it, but contributing little or nothing in return (para- 
sitism)] or the two organisms may maintain a loose or 
disjunctive symbiosis, which may be either (i) nutritive, 
as in those cases where ants cultivate filamentous fungi, 
maintaining fungus-farms; or (2) non-nutritive, as in the 
cases where certain plants like clover or orchids, are de- 
pendent upon insects for the transfer of pollen from one 
flower to another. These phases of symbiosis are indi- 
cated in the following table: 
Disjunctive or "social." 
(a) Nutritive (e.g., ants and fungus-farms). 
(b) Non-nutritive (insects and pollination). 
Symbiosis 1, . , .. 
2. tpiphytism. 
3. Mutualism. 
4. Parasitism. 
306. Social Symbiosis. As an illustration of social 
symbiosis of a nutritive character may be mentioned the 
interesting relation established between certain leaf- 
cutting ants and a filamentous fungus. The ants remove 
the foliage-leaves from certain trees and use them as 
"fungus-farms," or a suitable substratum on which to 
cultivate a certain fungus, portions of which serve as 
food for the ants (Fig. 232). The spores are sown by the 
ants and the "crop" harvested in a very systematic man- 
ner. The loss of leaves, however, is very deleterious to 
the life of the tree, and certain species (e.g., Cecropia and 
