JULY 23, 1897.] 
not improbable that such an examination would 
enlarge somewhat the variation in distribution 
as above given. Indeed, in another connection 
Apstein cites four catches made in Dobersdorfer 
See upon the same day, in which the variation 
from the mean is 100% or more, in three in- 
stances out of the four. This wide variation 
is, however, explained by our author as due to 
the presence of intervening sand bars in the 
lake. The results of counting individuals of 
various species in the plankton taken on the 
same day at different localities show a uni- 
formity less marked than that indicated by the 
volumetric determination. There is no indica- 
cation whatever of the presence in the plankton 
of ‘swarms,’ which Apstein defines as a local 
accumulation of animals of one species in one 
locality while the surrounding area is slightly, 
or not at all, peopled by it. This uniformity 
in the horizontal distribution is due to the simi- 
larity of the chemical constituents in the water, 
resulting in a uniform growth of the phyto- 
plankton and the zooplankton depending upon 
it. It is thus primarily a matter of food rela- 
tions. 
The vertical distribution of the plankton was 
determined by the subtraction process, and is 
subject to the error produced by the progressive 
clogging of the net. It seems very desirable 
that this problem be attacked by the pumping 
method. Apstein’s results indicate the accumu- 
lation of the greater part of the plankton in the 
surface stratum of 0-2 meters, in which from 
1} to 60 times as much plankton is found (per 
cubic meter) as is present in a similar volume in 
the water below a depth of 2 meters. In this 
particular his results are in harmony with those 
of Reighard, Ward, and Birge upon our own 
lakes. Most organisms prefer the surface waters, 
only a few rotifers and Entomostraca actively 
seeking the deeper and colder strata. The ver- 
tical distribution of many forms, especially 
among the phyto-plankton, is closely linked 
with the life cycle. The maximum numbers 
occur in surface waters, and as these decrease 
and resting stages appear, they seek the deeper 
water, to increase again and rise to the surface 
as the maximum returns. 
Apstein still maintains that plankton-rich and 
plankton-poor waters are characterized by the 
SCIENCE. 
141 
predominance of the Chrodcocacex and Dino- 
bryon respectively. Reighard has shown that 
these criteria cannot be adopted for Lake St. 
Clair, and later work is making it still more evi- 
dent that waters may be rich or poor in plank- 
ton quite irrespective of the conditions attend- 
ing such diversity in the lakes of Holstein. The 
suggestion that plankton-rich waters are occa- 
sioned by the abundance of water-fowl is of 
questionable value, though local data may seem 
to support it. 
Only those familiar with the routine of plank- 
ton investigation can appreciate the vast amount 
of work which Apstein’s book represents, 
though his results will command the attention 
of everyone interested in the cecological side of 
biology. The science of fresh-water planktol- 
ogy is stillin its infancy ; its methods are as yet 
imperfect, and its problems are so intricate that 
years of continuous investigation in a number of 
localities will be required to establish broad 
generalizations. Dr. Apstein has been a pioneer 
in the field, and the great value of his work lies 
in its exploratory character and in his sugges- 
tive mapping out of the problems of plank- 
tology. 
C. A. KorFoID. 
UNIVERSITY OF ILLINOIS. 
GEOLOGIC ATLAS OF THE UNITED STATES. 
FOLIO 25, LOUDON, TENNESSEE, 1896. 
THE Loudon folio, recently published by the 
U.S. Geological Survey, represents that portion 
of the Appalachian province which is situated 
between the parallels 35° 30’ and 36° and the 
meridians 84° and 84°30’. This area contains 
968 square miles, divided between Blount, Mon- 
roe, Loudon, Knox, Roane and Morgan coun- 
ties of Tennessee. 
The folio consists of a topographic map, a 
geologic map, structure sections, stratigraphic 
sections, a map of the economic resources, and 
descriptive text. The author is Arthur Keith. 
The text begins with a general description 
of the Appalachian province and points out the 
relations of this part to the others, with regard 
to its surface features. The local features of 
the drainage by the Tennessee river and its 
tributaries, Emory, Clinch, Tellico and Little 
Tennessee, follow next in description. 
