I 1920] AGRICULTURAL BOTANY. 131 



in cast' of zinc cultures. Increase in acidity of the nutrient solutidn siipplt'ini'Mts 

 the action of such heavy metals as zinc and iron. 



Salts of such stimulating heavy metals hydrolyze as a nilf in nn jHiMtous 

 solution, re.'fultinff in an increase of acidity which may he lendered more 

 effectiv'e tlirouf^h membrane concentration. Sodium silicate furnishes an ex- 

 ception to this rule of increase in acidity. Such progressive increase in the 

 acidity of a culture is largely a result of activities of the organism, and 

 may in turn be concerned also in the acceleration of growth and in the rctai'da- 

 tion of spore formation. 



The influence of phosphates on the action of alpha-crotonic acid on 

 plants, J. J. Skinner and F. II. Reii) {Amcr. Jour. Bot., 6 {W19), No. 4, pp. 

 J67-180, fujs. 9). — This investigation comprises a study of the effects of 

 a-crotonic acid on plants grown in pure water and in nutrient solutions com- 

 posed of phosi»hate salts with sodium nitrate and potassimu sulphate, a-crotonic 

 acid was i.solated fnmi soil characteristic of certain infertile spots near Mar- 

 shall, Tex., which have been incTeasing in size during observations extending 

 over several years, and wliich are herein briefly described as favorable areas 

 for an accumulation of organic acids. 



a-crotonic acid at strengths of 25 to 50 parts per million was found to reduce 

 growth from 35 to 50 per cent in case of wheat in nutrient culture solutions 

 of calcium acid phosphate, sodium nitrate, and potassium sulphates i)repared 

 according to the triangular system. Phosphates exerted an ameliorating effect, 

 regardless of the basic or acidic character of the salt. It is also claimed that 

 alkaline salts lessen the injurious inlluence of crotonie acid. 



The influence of lig;ht upon the action of stoniata and its relation to the 

 transpiration of certain grains, J. Gray and G. J. Peirce (Anier. Jour. Bot., 

 6 (1919), No. J,, pp. 131-155, figs. 18).— The authors find that the stomata of 

 barley, wheat, oats, and rye plants open with light and close with darkness, 

 variations in the light intensity exerting an influence witliin limits on the 

 i degree of stoma tal opening. 



Opening and closing being accomplished by the changes in the shape, of the 

 guard cells in the stomata, a minimum amount of moisture in the soil is re- 

 quired by eacli species in order to produce and maintain the turgidity of the 

 guard cells without which changes in their shape are impossible. The mois>ture, 

 soil, and light n'quirements of different species are essentially alike, though 

 not identical. 



Negative pressure and water utilization in transpiring shoots, M. Nord- 

 HAUSEN {Jahrb. Wiss. Bot. [rriii;ishcim], 5S {1917) . No. 2, pp. 295->ri5, fUin. 

 5). — The author considers that the force of coliesion, while sufficient to cause 

 considerable negative pi-essure, is not alone suflicient to meet observed normal 

 requirements of plants as regards water supply. 



Osmotic pressures in the potato plant at various stages of groAvth, B. F. 

 LuTMAN {Anicr. Jour. Bot., 6 {1919), No. 5, pp. lSl-202, figs. 2).— The iwtato 

 plant, early in the season, shows the highest osmotic pressure in the sap from 

 young stalks and leaves. During July and August, osmotic pressure in the 

 stalks is higher than that in the younger portions, this being due to the 

 presence of sugar, particularly cane sugar. In September, osmotic iiressm'e is 

 highest in the young leaves. Osmotic pressure of the sap in growing tubers is 

 always low, and that in the roots is the lowest in the plant. Osmotic pressure 

 in older is higher than in younger plants, due to larger amounts of inorganic 

 salts, but in very old plants it drops in consequence of partial removal of 

 soluble materials. 



Cell g,rowth in relation to supply of energy by protoplasts, .7. JM. .Tan.sp: 

 {Jiihrh. llisv. Hot. [I'riiigsht'im], 5S (1917), No. 2. pp. 221-236).— This is an 



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