Books and Cvrrent Literature. 99 



diflferent times, places, etc. with reference to their influence 

 on transpiration. It need hardly be added that the radio- 

 atmometer fails to take account of such secondary eff"ects of 

 light as stomatal movements, wilting and the like, which must 

 be studied by different means. 



The instrument here described is, then, a physical apparatus 

 which embodies some of the properties of plant foliage, being 

 affected in much the same manner as are plants by the two 

 aerial factors, evaporating power of the air and intensity of 

 radiation. Inasmuch as it adds photo-thermal effects to those 

 of the evaporating power of the air, the new instrument is to 

 be regarded as a better one for the study of these alterations 

 in rate of transpiration which have been supposed to be due 

 to purjioseful "regulation," than is the ordinary white atmo- 

 meter. Of course the water loss from different i)lant forms, 

 and even from different individuals, is not affected to the same 

 degree by conditions of the surroundings, and we need not ex- 

 pect to find the sunshine influence to be the same on all plants 

 as it is on the dark cup. Some plants exhibit a greater sensi- 

 tiveness to variations in solar intensity than do the cups, others 

 are less sensitive and others approximatelyequal one or the other 

 form of cup in their sensitiveness. We have here not only a 

 means for comparing radiation intensities at different times and 

 places, but also a method by which it should be comparatively 

 easv to study the relative sensitiveness of different plant forms 

 to the same variations in illumination. Such comparisons may 

 furnish a much-needed ballast of quantitative data to the dis- 

 cussion of xerophily and the like. 



The Johns Hopkins University. 



BOOKS AND CURRENT LITERATURE. 

 A California Sylva. — It is only a year ago that Jepson 

 gave us his "Trees of California," a manual adapted to popular 

 use, and he now crowns his studies in forestry with a noble 

 quarto * worthy of a place on the shelf by the side of vSargenfs 

 great Sylva. The excellent mechanical execution of the volume 

 is a credit to the Press of the University of California, and the 

 vast stores of information it contains are not only of the highest 



♦Jepson. Willi'; T.inn. Tlic Silva of California. Mem. Tniv. Cal. Vol 24to. pp 480. pis. 85, 

 maps 3. text figs 10. Berkeley, The University Press. (SlO.OOy. 



