284 THE AMERICAN NATURALIST. (VOL, XXXII. 
of Mendota is D. oregonensis, while that of Green Lake is D. minutus, 
a species of very different habits. It should be noted, too, that 
the Diaptomi are especially susceptible to the influences of the 
environment, and we must expect the different species to have their ` 
own peculiarities. 
He enumerates eight factors which determine vertical distribution, 
viz.: (1) food, (2) temperature, (3) condition of water in regard to 
dissolved oxygen and other substances, (4) light, (5) wind, (6) gravity, 
(7) the age of members of any given species, (8) specific peculiarities. 
Of these factors, the third is one of great importance, which has 
received very little attention from preceding authors. Professor 
Birge states that he is unable to state whether the lack of life in the 
lower waters of Mendota is due to a lack of oxygen or to a large 
amount of the products of decomposition. It has seemed to the 
reviewer that it was very probable that the products of decomposition 
have very much to do with the lack of life in many lakes, for, in an 
examination of a number of the Wisconsin lakes during the last 
summer, it was noticed that the deep lakes of small area had a large 
amount of organic matter on the bottom and almost an entire lack 
of animal life, while in the larger lakes with less organic matter 
there was a considerable abundance of animals. The other factors 
are discussed with considerable fullness. It is shown that gravity 
has a marked influence on the vertical position of crustacea, as it is 
only by considerable effort that they maintain their vertical position, 
and that, as they grow old or are enfeebled for any cause, they 
gradually fall to lower levels. Under seven it is shown that the 
young crustacea appear in greater numbers near the surface. The 
young of the copepods form an exception, however, for they appear 
in the greatest numbers near the thermocline. 
In conclusion, the reviewer must again express his regret that it is 
impossible to do justice to the paper within the limits of ordinary 
review, and considers that he has done as well as could be expected 
if he has succeeded in making evident the value of the investigation. 
BOTANY. 
Lessons with Plants.!— In recent years there has been a great 
multiplication of books designed to render the study of botany attrac- 
1 Lessons with Plants: ie se ae E Seeing and Interpreting Some of the 
Common Forms of Vegetation. By L Bailey. With delineations from nature 
