1907] CURRENT LITERATURE I4I 
English has had such a great sale, at least for many years. Very few changes 
are to be seen in the new edition. The frontispiece shows Professor DEVRIES 
at the Desert Laboratory in somewhat informal garb. The few errors of the first 
edition have been corrected, and some alterations have been made for the sake 
of clearness. The most important new feature is an explanatory note on varia- 
tions in Oenothera biennis. It is to be hoped that the sale of this second edition 
will also be great enough to necessitate the publication of yet another edition. 
In this way it will be possible for the general public to keep conversant with the 
rapid advance of our knowledge concerning mutation.—H. C. Cow es. 
HOTES FOR STUDENTS 
Fixation of atmospheric nitrogen.—In agricultural practice this is a most 
important matter; witness the many efforts to ‘secure it in leguminous crops 
by inoculating the soil. Two recent elaborate papers concern themselves with 
the organisms which are supposed to do this in the soil, and from these studies 
it is clear that our knowledge of this process and its conditions rests upon most 
insecure foundations. 
WARMBOLD, reviewing the literature relating to the alteration of the N-content 
of uncultivated soils, finds such a contradiction between the data, particularly 
those of BERTHELOT, who found N-fixation active in summer but nil in winter, and 
Koca, who found it notable in winter, that he endeavored to determine the con- 
ditions for the proceess in nature, especially in relation to temperature, water 
content of soil, aeration (dependent on porosity of soil), and the amount and 
character of organic substances present.2 Having carefully considered the 
sources of error in the methods of determining N in the soil, he believes his ana- 
lytic results may be relied on; and with a warning against too wide generalization 
from his data he concludes: (1) Well-aerated soils may be enriched in N without 
the intermediation of organisms, this having occurred in two series of experiments, 
while in three others under apparently like conditions it did not take place. 
(2) Temperature exercises no obvious influence, nor does water content, provided 
the soil is in thin layers and well aerated. When, however, it is in masses and 
contains less than 20 per cent. water, accumulation of N is either small or a minus 
quantity; at 10 per cent. there may be marked loss of N. This difference in 
behavior depends on a difference in the N-compound in question. With 3 per 
cent. water or less, the loss in N is due not to denitrification by organisms, but 
is purely chemical. In sterilized soil 3-20 per cent. of water has no effect; at 
30 per cent. N diminishes.*° (3) Aeration had no discernible effect in smal] masses 
of soil, but it was advantageous in larger quantities containing 15 per cent. 
_9 WARMBOLD, H., Untersuchungen iiber die Biologie stickstoffbindender Bak- 
Ein Beitrag zur Kenntnis der Veranderungen in Stickstoffgehalte des unbe- 
bauten Ackerbodens. Landw. Jahrb. 3521-123. 1906. 
1° But cf. as to this point SCHULZE on the effects of sterilizing soils. Abstract in 
Bor. GAZETTE 42:502. 1906. 
