ORGANOTOPIC PRANTS. 
107 
this vicinity, the former in almost any wood where leaf 
mold abounds, the latter usually under oak trees in rather 
dry woods. The white scapes and single nodding flowers 
of the Iudian pipe are familiar to every one—the brownish, 
several-flowered scapes of the false beech-drops are less 
frequently seen. 
As noted above, these two genera, Monotropa and Hy- 
popitys, represent the extreme of symbiotism in flowering 
plants. But the inference must not be drawn that all 
plants which have their root systems infested with fungi 
are necessarily decadent. The fact is, almost all forest 
plants, whether trees, shrubs or herbs, receive more or less 
nourishment from humus, or vegetable mold, and are ac¬ 
cordingly partial saprophytes. Many of them also receive 
the assistance of fungi, and are accordingly partial symbi- 
ots. Four large families of plants are now known to de¬ 
rive such assistance in the work of absorption. They are 
the pine, oak, birch and heath families. In them the work 
normally performed by root hairs is largely done by fungus 
l^phse and strands. These not only partially envelop the 
root, but they also*force themselves in between the cells of 
the tissue. A root thus infested has been called a fungus- 
root or mykorhiza. 
It is evident that the story of the dependent plants thus 
far is a story of greater or less degradation. Even before 
the true status of parasites was known the decadent tend¬ 
ency was recognized and such plants were supposed to be 
degenerate outgrowths from their hosts. A remarkable 
thing about dependent plants is that they lose entirely the 
external appearance of a vascular plant and even the whole 
structure of tissues characteristic of vascular plants, and 
yet retain unchanged the parts concerned in reproduction. 
A single organ, or parts of organs, may indicate the down¬ 
ward tendency more positively than the rest of the plant. 
The haustoria by which parasites attach themselves to and 
