PLANTS OF WESTERN LAKE ERIE. 
59 
in our lakes and streams. The vigorous growth and reproduction of plants furnishes 
a large food supply for the smaller animals, which in their turn can reproduce more 
abundantly and provide a greater amount of food for the fish. 
Barring enemies ancl artificial hindrances to increase, such as overfishing, fish 
will multiply up to the limit of the food supply, hut can never overstep that limit. 
If the food supply can be increased, an increase in the number of fish will naturally 
follow. 
PROBLEMS OF AQUATIC PLANT LIFE. 
To understand the factors controlling the primary source of food in th*e Great 
Lakes, we must study the plant life from every standpoint; we must learn the life 
history of each species, its physiology, distribution, and methods of reproduction. 
The important problems are, of course, physiological: The relations between the 
plant and the medium in which it lives; what it takes from the water and what it 
returns to it; the character of the bottom most favorable to certain species; the 
methods of passing the winter and of reproduction; the relations between the larger 
plants and the microscopic plant and animal forms that live on and among them, and 
the physical conditions of the lake — all these must be studied and, in great part, 
understood before we can determine what plants should be placed in a given lake 
and how we can best introduce them. 
These are some of the problems that most plainly present themselves and to 
which a study of the species found, together with their distribution, may be regarded 
as preliminary. This “taking an inventory,” as Zacharias aptly expresses it, is 
useful, but not final. We desire to know with what forms we have to deal, but the 
addition of a few more names to our list must not be thought of equal importance 
with a study of the life histories of these species.^ 
MACROSCOPIC AND MICROSCOPIC PLANT LIFE. 
The plant life of the Great Lakes may be roughly grouped into macroscopic and 
microscopic. It is exclusively the latter that enters into the plankton. These 
unicellular plants are the primary source of the food supply, their great reproductive 
power supplying a constant source of food for the plankton animals, which, in turn, 
feed the larger forms. 
Although the higher plants are not known to enter to any large extent into the 
diet of mature food-fishes, yet their importance in the economy of aquatic life must- 
be great because of the myriads of minute animal and plant forms that find shelter 
and subsistence among them. These forms— the insect larvae, mollusca, Crustacea, 
rotifera, and others — are important as fish foods, and their absence must adversely 
affect the distribution of fish. The importance of shore and bottom vegetation was 
recognized by Ward (loc. cit. ), who, in his report on the biology of the Traverse Bay 
region, makes constant reference to the scarcity of certain animal forms as due to the 
lack of plant life. The relative scarcity of hydra, worms, certain forms of rotifera. 
insect larvae, and mollusca he attributes to the lack of bottom and shore vegetation, 
and says: “The barrenness of the littoral zone eliminates from the question of the 
food supply of this region one element which in Lake St. Clair was of extreme 
importance.” This is recognized by Reighard (loc,. cit.), who makes frequent refer- 
ence to the abundance of certain animal forms in Lake St. Clair and connects it 
with the richness of the bottom flora. 
