Febetjakt 13, 1914] 



SCIENCE 



259 



the rate of transpiration, but in these experiments 

 relative humidity was also carefully studied and 

 a comparison between the time of day when the 

 lowest relative humidity occurred and the time of 

 day when evaporation and transpiration were 

 greatest. The rate of transpiration of leaves 

 taken at different heights was studied, together 

 with evaporation at the same heights. 



The laboratory experiments showed that the 

 rate of transpiration increased with wind veloc- 

 ity up to a certain limit, after which it did not 

 increase in proportion to the increase in wind ve- 

 locity. As a rule, in the field experiments trans- 

 piration was greatest before evaporation had 

 reached a maximum. 



The Effect of Certain Surface Films and Powders 

 on the Bate of Transpiration: B. M. Duggar 

 and J. S. CooLET. 



It is commonly observed that leaves of plants 

 sprayed repeatedly with Bordeaux mixture may 

 remain green and healthy, towards the close of 

 the season, several weeks after unsprayed leaves 

 free from fungous diseases have ripened. The ex- 

 perimental work reported up to this time has af- 

 forded no data indicating differences of sufficient 

 magnitude between the activities and imsprayed 

 leaves to account for the extended vegetative period. 

 The experiments here reported were made for 

 considerable periods of time with standardized 

 castor bean leaves in potometers and with large 

 numbers of potted tomato plants. Bordeaux mix- 

 ture, aluminium mixture, lime, and certain other 

 film-forming liquid and powders were employed. 

 In every case the rate of transpiration was 

 higher in the Bordeaux sprayed plants than in the 

 controls, or as compared with the standard. The 

 important differences make it necessary to give 

 weight to increased transpiration in any expla- 

 nation offered. 



The Belation Between the Transpiration Stream 

 and the Absorption of Salts: Heinrich Has- 



SELBRING. 



During the winter of 1908-1909 experiments 

 were conducted at Santiago de las Vegas, Cuba, 

 in order to determine the comparative transpira- 

 tion of tobacco plants under cheese-cloth shade 

 and in the open ground. For this purpose plants 

 were grown in galvanized iron tanks which were 

 set into outer encasing tanks permanently sunk 

 in the ground. Six tanks were placed among the 

 plants of a field of tobacco grown under cheese- 

 cloth, and six were set in an adjoining tobacco 

 field not shaded. The quantity of water trans- 



pired by the plants in the tanks was determined 

 by daily weighings, the quantity transpired being 

 replaced each day. At maturity the leaves, stems 

 and roots of each plant were harvested separately, 

 dried and ground. The ash was determined in 

 water -free samples of the ground material. From 

 the data the total ash of the plants was calcu- 

 lated. 



The plants grown in the open absorbed about 

 28 per cent, more water than those grown under 

 shade. The plants which absorbed and trans- 

 pired the greater quantity of water contained both 

 the smaller percentage and the smaller absolute 

 quantity of ash. 



It appears, therefore, that the absorption of 

 salts by roots is independent of the absorption of 

 water, and that the transpiration stream does not 

 exert an accelerating effect on the entrance of 

 salts. 



Belation of Transpiration of White Fine Seed- 

 lings to Evaporation from Atmometers: G. P. 

 Burns. 



An attempt was made to express the data re- 

 corded by meteorological instruments in terms of 

 plant physiology and thus give them a botanical 

 significance. The experiments were conducted in 

 the state forest nursery under different degrees 

 of ' ' shade. ' ' 



A comparison of the water loss from white 

 and black atmometers with that from white pine 

 seedlings under three conditions of shade used 

 gave the following coefficient of transpiration: 



^ , , -. f .0088 for black atmometer. 

 Half shade J. ..„„ „ , •. .. ^ 



[ .0087 ror white atmometer. 



f .062 for black atmometer. 

 ( .084 for white atmometer. 

 .036 for black atmometer. 

 .044 for white atmometer. 

 By use of these coefficients it is possible to calcu- 

 late the water loss from white pine seedlings from 

 the evaporation from the atmometers. 



Half shade reduces the transpiration and the 

 evaporation, but the graphs show that the response 

 of the plants and the atmometers is not identical. 

 The decrease in water loss due to "shade" for 

 the first part of August, 1913, was as follows: 

 black atmometer 50 per cent., white atmometer 

 44 per cent., white pine seedling 70 per cent. 



Plants grown under the three conditions studied 

 showed great variation in structure, in the amount 

 of ash, and their chemical composition. The 

 amount of water transpired by the no-shade 

 plants was many times that transpired by the 



No shade 



Full shade 



