460 



SCIENCE. 



[N. S. Vol. XV. No. 377. 



changes occur as one traces one type of 

 .edaphic formation upwards, these changes 

 are far less marked than are those observed 

 in passing from one edaphic formation 

 to another. Alpine, as well as all ecolog- 

 ical problems, can be ultimately settled 

 only by experimentation, and in this great 

 field Bonnier has led the way. The field 

 study of ecology should be regarded chief- 

 ly in the light of furnishing an intelligent 

 basis for experiment. Illustrated by lan- 

 tern slides. 



R. A. Harper : ' Cell Division in Cer- 

 tain Blue-Green Algte. ' (No abstract fur- 

 nished. ) 



C. R. Barnes : ' The Significance of 

 Transpiration.' In this paper the author 

 seeks to present a new point of view re- 

 garding transpiration, taking account of 

 the extensive results of experimentation 

 already attained. The purpose of trans- 

 piration is ordinarily held to be double: 

 (a) to cause the influx to the leaves of a 

 large quantity of water, that thereby a 

 sufficient amount of mineral salts may be 

 supplied to the leaves; (&) to concentrate 

 the extremely dilute solutions thus brought 

 to the leaves and so get rid of surplus 

 water. These two phases of the function 

 are held by the author to be, to some de- 

 gree at least, mutually exclusive. The 

 amount of salts absorbed is certainly de- 

 pendent upon the living cortex of the root- 

 lets and the mesophyll of the leaves. (For 

 the purpose of the present discussion the 

 xylem bundles may be conceived as fur- 

 nishing no obstacle to water flow.) If the 

 cortex be freely permeable, equilibrium in 

 the distribution of any given salt will oc- 

 cur, assuming for a time no evaporation 

 from the aerial parts. If then evapora- 

 tion concentrates the solution the higher 

 diffusion tension of that salt will tend to 

 drive it to those regions where the diffu- 

 sion tension is lower. This tendency. 



therefore, would operate against the fur- 

 ther supply of that material to the leaves. 

 If the cortical layers be not freely perme- 

 able, the amount absorbed is regulated 

 wholly by protoplasmic activity and can- 

 not be affected directly by the outside sup- 

 ply. The phenomena of selective absorp- 

 tion show that transpiration does not 

 determine in these eases the amount of 

 salts absorbed. The significance of trans- 

 piration is to be discovered by examining 

 its origin and tracing its development. 

 Under the present organization of plants- 

 exposure of wet cell walls to the atmos- 

 phere is indespensable for the solution of 

 necessary gases, oxygen and carbon dioxid,. 

 the plant being debarred from water- 

 proofing the cell wall so long as gas ab- 

 sorption is necessary. Transpiration is,, 

 therefore, considered as unavaidahle^ 

 though in itself a constant menace to life 

 and activity. Advantage has doubtless 

 been taken of the xylem bundles to facili- 

 tate the movement of solutes, but there is. 

 no reason to think this essential. Trans- 

 piration also has become a protective fac- 

 tor with sun plants, whose temperature is 

 thereby kept \vithin reasonable bounds. 

 (Since reading the paper the author haa 

 ascertained that in certain points his view 

 of transpiration coincides with those ex- 

 pressed by Dr. C. E. Bessey in a paper on 

 the function of stomata, published in 

 Science, N. S. 7: 13-16. 1898.) 



R. A. Harper : ' Binucleate Cells in Cer- 

 tain Hymenomycetes. ' (No abstract fur- 

 nished. The paper is published in full in 

 the Botanical Gazette 33 : 1-25. pi. 1. 

 1902.) 



James B. Pollock : ' An Abnormal De- 

 velopment of the Prothallium of the Pollen 

 Grain in Picea excelsa.' The author re- 

 ported a ease of a pollen grain of Picea ex- 

 celsa in which there were four cells formed 



