1917] AGRICULTUEAL BOTANY. 525 



The nature of mechanical stimulation, W. J. V, Ostekhout (Proc. Nat. Acad. 

 Sci., 2 (1916), No. 4, pp. 237-239, fig. i).— The author observed that when a cell 

 of the marine alga Grifflthsin bonietlana was touched near one end, the surfaces 

 of the chromatophores in this region became permeable to their red pigment. 

 This soon began to diffuse out into the surrounding protoplasm, rendering the 

 other chromatophores, as successively reached, permeable in like manner, a 

 wave of stimulation thus progressing until the other end of the cell is reached 

 by the wavelike changes. It is thought that the alterations set up in the suc- 

 cessive cells, resulting in diffusion of red pigment (and probably other sub- 

 stances), are chemical in their nature. 



The disturbance is thought to originate as a mechanical rupture of the sur- 

 face layer of the chromatophore, as a nximber of cellular structures are known 

 to possess surface layers of great delicacy. Reactions are supposed to occur 

 between the diffused contents and other substances as encountered. Physical 

 alterations in the pi'otoplasm may thus give rise to chemical changes, and re- 

 sponses to contact and mechanical or gravitational deforming stimuli may thus 

 be explained. In this conception of mechanical stimulation the essentials are 

 substances separated by semipermeable membranes, production of a rupture 

 in these which is not at once repaired, and a resulting reaction which produces 

 the characteristic visible respon.se to the stimulus. 



Energy transformations during the germination of wheat grains, Lucie C. 

 DOYEK {Rec. Trav. Bot. Neerland., 12 {1915), No. 4, pp. 369-423, pis. 2).— Giving 

 a bibliography and more extensive data than in a previous report (E. S. R., 

 35, p. 632), the author states that in the germination of wheat grains the loss 

 of energy increased for seven days, particularly on tlie third day. The loss 

 during the first two days, when imbibition was relatively important, was com- 

 paratively small. 



Heat evolution also increased with the progress of germination, the increase 

 being most marked on the third and the fourth day, and the rate being increased 

 with a rise of temperature up to 35° C. (95° F.), the heat development more 

 than doubling with a rise of 10°. At 40° heat development began to diminish. 

 Respiration was increased during germination at a temperature of 25°, the 

 increase being greater in the early period of germination. During the first 

 six days of germination at 25° the amount of heat given up was less than the 

 loss of energy set free by respiration. Heat development had its optimum at 

 35°, which is higher than the optimum for respiration. There appears, there- 

 fore, to be no constant relation between heat development and respiration. 



A study of the relation of soil moisture to transpiration and photosyn- 

 thesis in the com plant, T. G. Yunckee (Plant World, 20 (1916), No. 6, pp. 

 151-161, figs. 4). — Experiments to determine the relation between the amount 

 of transpiration and photosynthesis in corn plants and the degree of soil mois- 

 ture in which they were grown are described. 



The author reports, in regard to three tests made, that the plants in soil 

 watered to 25 per cent of saturation weighed the most per unit of leaf area, 

 those in that at 65 per cent the least, while those at 45 per cent showed an 

 intermediate increase of weight and inferentially of photosynthetic activity. 

 The water requirement was less for plants in the drier than for those in the 

 wetter cultures. Transpiration rates showed the same relation to moisture 

 content as did the water requirement. It thus appears that the amount of 

 organic matter formed is not proportional to transpiration. 



On the relation between the rate of root growth and oxygen, W. A. Can- 

 non (Abs. in Science, n. ser., 44 (1916), No. 1143, p. 761). — A series of experi- 

 ments is reported in which the roots of Pi'osopis velutina and Opuntia versi- 



