440 The American Naturalist. [May, 
acters. Many suggestions are made to explain this, such as: in regions 
of high latitude or altitude, xerophilous characters lessen evaporation 
early in the season, when the roots are inactive, due to cold soil; or 
the activity of the roots is hindered by the difficulty of aeration, hence 
the need of lessened eporenens or, sin since = stomata remaining 
open, cannot regulate necessary- 
The most probable explanation of the presence of peiertprs char- 
acters in halophytes is that the roots have difficulty in obtaining water 
from the strong solution of salts in which they are placed, hence the 
necessity of lessened evaporation. 
The closing section treats of the struggle between the various plant 
communities. 
he book should be read by every student of ecology ; but more, the 
general reader would be amply repaid by its perusal. It is to be hoped 
that the book may be translated into English.*—A. 8. HITCHCOCK. 
ZOOLOGY. 
The Gas of the Natatory Vessels of Physalia and of Fishes.’ 
—As a result of a search’ for argon in the natatory vessels of Physalia 
and of fishes there were found in the vessel of the former (Physalia 
pelagica Lk) from 85-91 per cent. of nitrogen, and from 9-15 per 
cent. of oxygen, but no other gas. Intheswimming bladder of surface 
fish (Polyprion cernium Val.) there was found about 80 per cent. of 
nitrogen, 18 per cent. of oxygen, and 2 per cent. of carbonic acid gas, 
while in deep sea forms, such as Murena helena, taken from a depth 
of 88 meters, and Synaphobranchus pinnatus Gr., taken from a depth of 
1385 meters, 3-6 per cent. of carbonic acid gas and oxygen in the large 
amount of 73-85 per cent. were found. 
The Genus Ascaris.—In his monographic work? devoted to this 
genus of worms, Stossich considers 218 species. Of this number 35 
*An English translation of this book is now in preparation and will be pub- 
lished by Macmillan.—Eb, 
1 Richard A. (96). Sur les gas de la vessie natatoire des poissons et des physa- 
lies. Bull. Mus. Hist. Nat., Paris, 41-3. 
2 Schloesing, Th., and Richard J. (96). Recherche de l'organ dans les gas de 
la vessie natatoire des poissons et des physalies. Compt. Rend. Ae. P., cCxxII, 
615-7. 
Zool. Centralbl., IV, 1 
3 Bull. Soc. Adriat. te Nat., Trieste, XVII (1896), pp. 7-120. Zool. Cen- 
tralbl., IV (1897), p. 20. 
