NOTES AND ABSTRACTS. 
499 
"black-leaf 40," kerosene, and gasoline, and in all cases plants grown in the 
treated soils contracted the root-knots so characteristic of the disease. Carbon- 
bisulphide, strong formaldehyde solution, and tobacco stems greatly reduce 
the number of nematodes in the soil, and the author believes that treatment 
with such chemicals might be of value in the case of rapidly -growing crops « 
With such crops as ginseng — a crop which occupies the ground for as long as 
six years — the treatment would be worthless, as the nematodes left in the soil 
would completely repopulate it within a very short time. He concludes that 
"in the light of these experiments, no chemical could be recommended for the 
control of root-knot nematodes." 
Theories as to the failure of the field experiments are next set forth, and a long 
series of experiments on the action of various chemicals on the eggs is recorded. 
Of the numerous chemicals experimented with, it was found that in no case were 
the eggs prevented from hatching, and this fact, amongst others, is given as a 
possible reason for the failure of the chemical treatments in the field experiments. 
Circumstances did not permit of the author conducting complete experiments on 
the control of Heterodera by steam sterilization, but he is of the opinion that 
the nematodes are killed by a thirty-minute treatment with steam at a pressure 
of eighty pounds. The results of these experiments are not sufficiently conclusive 
for the author definitely to recommend this treatment. — /. K. R. 
Nitrogen-fixing Organisms of the Soil, The Effect of Arsenic upon the. By 
J. E. Greaves (Jour.Agr. Res. vol.vi. No. 11, June 1916, pp. 389-416; 5 figs.). — 
The author finds that arsenic, when applied to a soil in the form of lead arsenate, 
sodium arsenate, arsenic trisulphide, or zinc arsenite, stimulates the nitrogen- 
fixing powers of the soil. This stimulation is greatest when lead arsenate is 
applied, and least when zinc arsenite is applied. Paris green did not stimulate 
in any of the concentrations. This compound becomes very toxic when the 
concentration reaches 120- parts per million, and the toxicity of this compound 
is due to the copper, and not the arsenic contained in it. Sodium arsenate 
became toxic when a concentration of 40 parts per million of arsenic was reached, 
and when 250 parts per million were added it entirely stopped nitrogen fixation. 
Lead arsenate was not toxic even at a concentration of 400 parts per million 
of arsenic ; while the toxicity of arsenic trisulphide and zinc arsenite were very 
small at this concentration. 
The stimulation noted was not due to any inherent peculiarity of the soil 
used ; for soils which vary greatly in physical and chemical properties had 
their nitrogen-fixing powers greatly increased when arsenic was applied to them. 
Only one type of Azotobacter was isolated which was stimulated by arsenic, 
and in this case the stimulation was due to the organism utilizing more economi- 
cally in the presence of arsenic its source of carbon than it did in the absence 
of arsenic. The stimulation noted is due largely to the arsenic inhibiting 
injurious species. 
Arsenic stimulates the cellulose ferments, and these in turn react upon the 
activity of the nitrogen-fixing organisms. 
A fairly complete bibliography is appended. — A. B. 
Nitrogen in Certain Legumes, A Biochemical Study of. By Albert L. Whiting 
(U.S.A. Exp. Stn., Illinois, Bull. 179, March 1915, pp. 471-542 ; 17 plates, 
6 figs.). — The experiments show that the cowpea and soy bean utilize atmospheric 
nitrogen through their roots, not through their leaves. No combined nitrogen 
could have been assimilated in these gas experiments. The total nitrogen 
determination shows that 74 per cent, of the nitrogen of cowpeas and soy beans 
at the time of harvest is in the tops, while the remainder is distributed between 
the roots and the nodules. In the earlier periods the roots contain the larger 
part, while later they contain much the smaller part. 
The percentage of soluble nitrogen in soy beans and cowpeas varies with the 
different parts of the plant and with the period of growth. On an average the 
soluble nitrogen in the tops was 45 per cent, of the total ; in the roots 34 per cent. ; 
in the nodules of soybeans 14 per cent., and in nodules of cowpeas 34 per cent. 
Phosphotungstic acid usually precipitates some form of nitrogen. In these 
experiments the amounts of nitrogen so precipitated averaged 12 per cent, in 
the tops of both soy beans and cowpeas ; 5 per cent, in the roots ; 1 percent, in 
the nodules of soy beans ; 17 per cent, in nodules of cowpeas. Other forms of 
soluble nitrogen occur which are not precipitated by phosphotungstic acid. 
Fixation takes place at a very early period in the growth of the seedling — 
sometimes within 14 days. It is rapid in the case of the cowpeas. 
Plants grown under the conditions of these experiments contain no ammonia 
nitrites or nitrates, as measured by the most accurate chemical methods. — A . B. 
