306 Morphologie etc. — Physiologie. 



feilos konstatiert ist. Die anderen Fälle beziehen sich auf zwei' 

 Toddalieen, Phellodendron amurense Rupr. und Ph, japonicum Max. 



W. Herter (Berlin-Steglitz). 



Briggs, L. J. and H. L. Shantz. Hourly transpiration rate 

 on clear days as determined by cyclic environmental 

 factors. (Journ. agric. Research. Washington. V. p. 583—649. 

 1916.) 



With an extensive description of apparatus and methods for 

 measuring of transpiration and of physical factors, the paper gives 

 a great many results of these measurements and the different rela- 

 tions between them. The plants experimented with, included wheat, 

 oats, rye, sorghum, alfalfa and amaranthus; they were grown in 

 large sealed pots of the type used in water requirement measure- 

 ments, containing sufficient soil (about 115 KG) to enable the plants- 

 to make a normal growth. The transpiration was determined by 

 weighing, four automatic platform scales recording each 20 gm-loss 

 being used for the purpose. Automatic records were simultaneously 

 made of the radiation intensity, the air temperature, the depression, 

 of the wet-bulb thermometer, the evaporation and the wind velocity. 

 The radiation intensity and the wet-bulb depression were measured 

 by differential telethermographs, and the evaporation rate from a 

 free-water surface was determined by mounting a shallow, blackened 

 evaporation tank 3 feet in diameter on an automatic platform scale. 



Composite graphs are presented, showing the main hourly 

 transpiration rate for each of the plants considere^, together with 

 the mean hourly values of the radiation, air tempera'ture, wet-bulb 

 depression, and wind- velocity for the transpiration period and also 

 the mean hourly evaporation rate. On the basis of the form of the 

 curves the transpiration graphs may be grouped into two classes 

 having characteristic features. The cereals show a marked change 

 in the slope of the transpiration graph in the forenoon unaccom- 

 panied by corresponding changes in the environmental factors. On 

 the other band, the forage plants and amaranthus gave little or no 

 indication of such a change. This flattening of the graphs in the 

 case of the cereals appears to be due to some change in the plant, 

 resulting in a reduction in the transpiration rate below what would 

 be expected from the form of the curve during the early morning 

 hours. 



The hourly transpiration rate of the cereals on clear days in- 

 creased steadily, though not uniformly, from sunrise to a maximum 

 value, usually reached between 2 and 4 p. m., after which it feil 

 rapidly to the night level. The transpiration graphs for sorghum j. 

 alfalfa and amaranthus were somewhat more symmetrical with re- 

 spect to midday, reaching their maximum between noon and 2 p. 

 m., after which they feil approximately with the radiation. 



The transpiration during the night at Akron (Colorado) 

 where the experimenis had been made, is very low, being only 3 

 to 5 percent of the transpiration during the daylight hours. 



The radiation graphs are practically symmetrical with respect 

 to noon, showing that the days selected were relatively clear. 

 When all the mean hourly values are expressed as a percentage of 

 the maximum, the radiation intensity rises in advance of the transpi- 

 ration (and in advance of all the other environmental factors as 

 well) and falls either in advance of the transpiration or with it^ 



