

326 BOTANICAL GAZETTE [april 



City the moss flora of the north and of the south meet and mingle, and the 

 number of species occurring is large, varied, and interesting/' — J. M- C. 



NOTES FOR STUDENTS 



Transpiration studies. — Among several recent papers dealing with various 

 phases of the study of transpiration, a prominent place should be given to one 

 by LIVINGSTON and Shreve 6 upon improvements in the use of the cobalt 

 chloride paper method. An improved paper slip has been designed which 

 combines two permanent color standards and an area of carefully prepared 

 cobalt chloride paper. The determinations of the end points are made more 

 definite, therefore, and the probability of error is much reduced. An improved 

 device for furnishing a standard water surface is described also. The temper- 

 ature relations of the rate of color change in the hygrometric paper and its 

 permanent standardization is discussed also. These improvements will 

 greatly advance the method of study which has already been proved 

 valuable. 



Another modification of methods of study is seen in Darwin's 7 investi- 

 gation of the relation of transpiration to relative humidity by the porometer 

 method, using Primus Laurocerasus and eliminating the action of stomata by 

 applying vaseline to the lower surface of the leaves and then placing their inter- 

 cellular spaces in communication with the external air by means of incisions. 

 Plotting the results, he found that transpiration varies directly as relative 

 humidity when a correction is made for the fact that the transpiration rate is 

 not zero in saturated air. The fact that transpiration does occur in saturated 

 air is due, as pointed out by Sachs, to the production of heat in the leaf by 

 respiration. The experiments show T ed that for the transpiration to be entirely 

 checked a humidity of 5 per cent above saturation would be necessary, and 

 hence the temperature of the leaf due to respiration is, under the conditions of 

 the experiments, o?8C. above that of the atmosphere. 



Using similar methods and materials, Darwin 8 also studied the effect of 

 diffuse light upon transpiration. The results show so remarkable an amount 

 of variation that it seems dangerous to draw any conclusions other than that 

 light tends to increase the water loss for some unknown reason when its influ- 

 ence upon the action of stomata has been eliminated. This increase averages 

 about 33 per cent. 



6 Livingston, B. E., and Shreve, Edith B., Improvements in the method for 

 determining the transpiring power of plant surfaces by hygrometric paper. Plant 

 World 19:257-309. 1916. 



7 Darwin, F., On a method of studying transpiration. Proc. Roy. Soc. London 

 B 87:269-280. 19 14. 



8 ^ xhe effect of light on the transpiration of leaves. Proc. Roy. Soc. 



London B 87:281-299. 1914. 



