60 TRANSACTIONS OF THE [Sess. lxxx 



Sorauei- (Forsch. a. d. Gebiet der Agrikultur Physik 

 von Wollny, Bd. iii, 1880, p. 351) observed a maximum of 

 transpiration in the late forenoon and early afternoon, and 

 a minimum before sunset. 



Baranetzky (Bot. Zeitung, tom. xxx, 1872, p. 65) denies 

 the existence of a periodicity, and is of the opinion that 

 the plants transpire more during the night than in the 

 daytime, mentioning that the loss of water is steady but 

 not periodic. 



Eberdt contradicts Baranetzky "s views from the results 

 of his own experimental work. 



More recent research on periodicity in transpiration 

 has been carried out by G. C. Curtis (Bull. Torrey Club, 

 tom. xxix, 1902, p. 363). Curtis took weighings every hour 

 for a period extending over twelve hours or less, and the 

 temperature and humidity of the laboratory were kept as 

 constant as possible. He obtained a maximal value for 

 transpiration about the middle of the day, and minor 

 fluctuations independent of the light intensity were also 

 recorded. Experiments were performed under normal 

 conditions in constant illumination and in the dark. He 

 found that the curve in the dark sometimes was in keeping 

 with that obtained under constant illumination, but it was 

 more often very erratic. The graphs obtained by Curtis 

 for transpiration resembled Sachs' curve for growth, 

 Vesriue's curve of absorption, and Detmer's curve for the 

 per-iodicity of exudation of fluids from cut stems and fluid 

 tensions. The transpiration graphs obtained by Curtis 

 varied for every plant experimented upon, and for the 

 same plant no two graphs were ever alike. 



In order to have more positive proof of the phenomenon 

 of periodicity, it was nccessai-y t(j procure graphs of at 

 least twenty-four hours' duration, and tor this purpose the 

 apparatus already described at the June meeting of tlie 

 Society, 1J)15, was used.' 



'I'lie plants experimented upon were 



1. Piiiiii^ si/lve.sfrls. 



2. () 11)1 III Id (ici'idc iihil IK. 



3. Jjil Ill-Ill. riihrniii. 



' Sf;e Trans. l!ot. Soc. I'Miii., .\.\vi (liilT)), 4.3:^. 



