AGRICULTUKAL BOTANY. 331 



variant factors, preventing their full expression in augmented crops. Tlie 

 point wbere this interference begins is rlifflcult to determine. The law of 

 minimum is a straight line function only so long as optimal vegetative factors 

 operate. Larger water utilization affects the relative solid content of crops 

 negatively. About 364 gm. of water was used per gram of dry substance formed 

 above ground. 



Relation of the daily march, of transpiration to variations in the water 

 content of foliage leaves, B. E. Livingston and W. H. Brown {Bot. Gas., 53 

 (1012), No. Ji, pp. 309-330). — ^Attention was called in a previous publication 

 (E. S. R., 18, p. 328) to differences existing between the time of the maximum 

 evaporating power of the air and the maximum transpiration in certain plants. 

 From a study of the relation of transpiration to variation in the water content 

 of leaves the authors conclude that there can remain little question that green 

 plants when subjected to relatively great diurnal evaporation intensity fre- 

 quently exhibit a marked fall in foliar moisture content 03^ day and a corre- 

 sponding rise by night. 



The experiments reported wei-e made in Arizona and the authors were unable 

 to compare the conditions with those of more humid and cooler regions. It is 

 stated that, so far as evidence is at hand, it is probable that the cause of this 

 diurnal minimum in foliar moisture rests in the phenomenon of incipient dry- 

 ing, brought about wherever the ratio of water loss to water supply in the 

 leaves is rendered less than unity. Although the experiments would seem to 

 indicate that the external factor which controls this diurnal fall of leaf moisture 

 is evaporation intensity, the true controlling condition, the authors believe, is 

 more probably the ratio of water supply to water loss. The structure of the 

 plant, the moisture conditions of the soil, and the intensity of evaporation and 

 of solar illumination appear to make up the controlling environmental complex. 



It is thought probable that the diurnal, nonstomatal retardation of the escape 

 of water vapor from green leaves in sunlight is the effect of a lower vapor 

 tension within the internal atmosphere of the leaves and over their surfaces. 

 This lower A-apor tension is brought about by the increased surface tension and 

 decreased evaporation surface which accompanies a lowered water content of 

 the internally and externally exposed cell walls. 



The authors think that in the diurnal minimum in the water content of 

 foliage leaves a criterion can be established that may prove of importance to 

 scientific agi'iculture, in arid regions at least. By this it may be possible to 

 determine indirectly and somewhat simply the status of the water relations of 

 the plant and to foresee the need of increased soil moisture long before the 

 cessation of growth or actual wilting becomes manifest. 



Stimulation movements of plants, B. G. Pringsheiai (Die Reisheicegiingcn 

 iler Pflansen. Berlin, 1912, pp. VIII+326, figs. 96) .—This book is intended as an 

 introduction to the study of the physiology of stimulation in plants, being some- 

 what moi'e full than the treatment usually given in text-books but not so de- 

 tailed and specialized as that found in more technical treatises. Free move- 

 ment, protoplasmic streaming movements, growth and turgor movements, and 

 the various tropisms receive separate and proportional discussion. The work 

 concludes with a somewhat full bibliography and an index. 



Nitrogen assimilation under sterile conditions of plants from nitrates, 

 ammonium salts, and asparagin, G. G. Petrov (Isv. Moskov. Seisk. Khoz. Inst. 

 (Ann. Inst. Agron. Moscou), 17 (1911), No. 4, pp. 141-178, figs. 3). — The in- 

 vestigator cultivated maize plants on nets suspended in sterile tubes in a stream 

 of carbon dioxid over nutritive solutions of (1) calcium nitrate, (2) ammonium 

 sulphate, and (3) asparagin. Both stalks and roots were analyzed, and deter- 

 minations were made of the total nitrogen content, also of that found as 



