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CURRENT LITERATURE.
Physiology.
Gardner, VV. W. and AUard, H. A. Effect of the Relative Length of Day and Night and Other Factors on Growth and Reproduction in Plants. Jour. Ag. Bes. IS. 11. 1920.
The length of the day is one of the most important factors in determining the periodicity of plants as regards vegetative or reproductive development. It far out-weighs in importance such factors as temperature, moisture supply or actual amount of light.
The authors carried on extensive experiments with plants grown in receptacles which could be moved at will from daylight into dark chambers. Shortening the day affected different plants differently. Some had their flowering period brought on more quickly and some had their vegetative period indefinitely prolonged and became gigantic in size. Some species when exposed to relative day and night lengths favourable to both growth and re- production assumed an " ever-blooming " type of development, the two pro- cesses of growth and reproduction proceeding together for an indefinite period.
The seasonal range in the length of the day is an important factor in the natural distribution of plants. Its influence probably accounts for the frequent failure of plants to thrive when removed through a wide range of latitude. Note for example the frequently unsatisfactory behavior of English-grown vegetable seeds in India.
This work suggests possibilites to the horticulturist who would plant at the season which will enable his crop to secure the highest benefit of seasonal day and night length. It also suggests as has since been demonstrated in a practical way, that the greenhouse grower may control his product, hasten- ing or prolonging its maturity, by the simple control of this factor.
L. A. K.
Chilcott, E. C. and Cole, John S. Sub-soiling, Deep Tilling and Soil Dynamiting in the Great Plains. Jour. Ag. Bes. 14. 11. 191S-
The belief is general that deep tillage or the use of explosives enables the roots of a crop to penetrate more deely into the soil and helps the crop to overcome drought. Careful experiments were carried out with these processes on various parts of the Great Plains region of the United States, and the yield determined in the case of various crops grown in that region. In some cases the special treatment showed a benefit, but this benefit was by no means general and in almost no case was it sufficient to pay the increased cost of the treatment. In seasons which owing to drought are below the average in productivity, breaking the sub-soil appears to reduce the yield. Experiments performed in various parts of America, humid and arid, and in semi-arid Southern Russia give conclusions which in general agree with those of the authors.
L. A. K.
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