1922] CURRENT LITERATURE 247 
content of the plant. The elements, the amount of which present in the nu- 
trient solutions was varied, were calcium, magnesium, potassium, phosphorus, 
and nitrogen. The plan was to reduce the amount of these elements present 
to.the lowest concentration that would allow the production of grain. This 
concentration would be’ below that required for the normal development of the 
plant, and it was thought that in such conditions the effect of the elements on 
the composition of the plant would be more strikingly brought out. Aside 
from the greatly reduced calcium or phosphorus content, when the amount 
of these elements in the respective nutrient solutions was reduced, the most 
striking results obtained were the low calcium content of the plants of the low 
phosphorus series and the low nitrogen series, and the high phosphorus content 
of the plants of the low calcium series and the low nitrogen series. Potassium 
d magnesium seemed to have little effect on the calcium and phosphorus 
content of the plant. Climatic factors, on the other hand, were shown to have 
a decided effect on the composition of the plant. A good bibliography is 
added.—S. V. Eaton 
Alkali soils —The hardening of irrigated land has been studied by SCOFIELD 
and HEADLEY," who conclude that neutral salts of sodium as well as the 
carbonate, “black alkali,” may produce hardening of the clay component of 
soils. The results are about the same, whether sodium-containing water is 
used on good soils, or whether pure water is used on salty soils; in either case 
the soil will harden seriously on drying, and become somewhat impervious 
to water. The theory advanced to explain the action of sodium on clay is 
that the sodium replaces other bases on the surface of the particles, and becomes 
in part sodium silicate. This hydrogel coating increases the effective size 
of each particle, reduces the porosity of the soil, and greatly retards water perco- 
lation through it. On drying, the colloidal gel cements the particles — 
whence the hardness of these soils. If enough calcium or aluminium is prese 
however, the harmful action of sodium is obviated. When irrigation see 
contains more Na and K together than Ca and Mg, it is likely to cause harden- 
ing. The Colorado River and its lower tributaries contain too much of the 
hardening salts. The authors think injury to irrigated land may be avoided 
by treatment of irrigation water or land with soluble calcium or aluminium 
Its.—C. A. SHULL. 
Nitrogen fixation by green plants.—WANN" presents some. interesting 
results of experiments showing that members of the Chlorophyceae can utilize 
the uncombined nitrogen of the atmosphere. Seven species exhibited this 
*6 ScoFIELD, C. S., and Hraptey, F. B., peed . — water in relation to 
land reclamation. Jour. Agric. Res. 21: 265-278. 1 
™ WANN, F. B., The fixation of free nitrogen ae green plants. Amer. Jour. Bot. 
8:1-29. pl. 1. fig. 1. 1921. 
