ASSOCIATED PLANTS AND ANIMALS 503 
in pollination and dissemination of fruits and seeds. In 
regions where there are strong prevailing winds only such plants 
as are adapted to regulate transpiration can grow. Most of our 
early flowering plants, as the Pines, Oaks, Beeches, and Poplars, 
are pollinated by the wind, and some of our crop plants, as Corn 
illustrates, depend largely upon the wind for pollination. For 
the wide dissemination of the fruits and seeds of many of the 
common weeds and of some cultivated plants, and also for the 
spreading of some fungous diseases the wind is responsible. 
Associated Plants and Animals.— A plant must compete 
with surrounding plants and often with animals for existence. 
It is common observation that most crop plants will not do well 
under the shade of trees. The trees cut off the light and make 
the soil too dry for the crop plants. On the other hand, there 
are plants which require shade and hence grow best in the woods. 
In some cases plants are benefited while in other cases they are 
injured through the association of their roots with the roots of 
other kinds of plants. For example, when Corn and Clover 
are grown together, experiments indicate that Corn does better 
than when it is grown alone. One experimenter grew Oats, 
Barley, Buckwheat, Wheat, and Flax in pots with and without 
the underground shoots of Canada Thistle and found all except 
Buckwheat to grow better with the Canada Thistle than alone. 
He repeated the experiment, using a young Elm tree instead 
of the Canada Thistle, and found that all grew more poorly with 
the Elm tree than alone. In Jutland it is found that Spruce 
trees grow well on waste areas if their roots can associate with 
those of the Mountain Pine. If there are no Mountain Pines 
present, the Spruces will not grow. If the Pines are present 
but are cut before the Spruces get well started, the Spruces die 
or make a poor growth. No doubt much injury to crops caused 
by weeds is due to the antagonistic effects of their root systems. 
The association of certain kinds of nitrogen-fixing Bacteria 
with the roots of legumes and of parasitic plants with their 
hosts are familiar examples of a very intimate relation of the 
life processes of one plant with those of another. Jn competing 
for light, as previously pointed out, plants must adjust themselves 
to each other in various ways. Climbing plants, in securing a 
better position in reference to light for themselves, frequently 
injure the plant which they climb. For example, Morning 
