TRANSPIRATION OF WHITE PINE SEEDLINGS 3 



The final answer to questions raised by the ecologists can only 

 be found by experimental work, as in any other line of botany. 



During the past three seasons the writer has been studying 

 the evaporation from porous cups placed in seed beds in the 

 Vermont State Forest Nursery, and the present paper is an at- 

 tempt to express the results of evaporation from the white and 

 black atmometers in terms of transpiration from the seedlings of 

 Pinus strobus. 



It is not necessary to describe in detail the seed beds. The 

 usual nursery bed was used. These are 12 feet long, 4 feet 

 wide surrounded by a frame 1 foot high. Three kinds of covers 

 were used. One was covered with wire; a second, half covered 

 with lath; and a third, entirely covered with lath. In each 

 bed were placed black and white atmometers. The amount of 

 transpiration was determined by weighing plants which had been 

 previously potted. The data recorded represents the result of 

 15 four-hour periods during the first half of August, 1913. 



The effect of external conditions upon the various objects 

 used in the experiments showed only a general agreement be- 

 tween evaporation and transpiration. In the no-shade, half- 

 shade and full-shade beds the agreement of the atmometers was 

 rather striking. In comparing the plants with the atmometers, 

 it was seen that although the response was not similar, yet there 

 was a closer relation between the black atmometer and plants 

 than between the white atmometers and the plants. 



Using the black atmometer as a basis for comparison, it was 

 found that the relative transpiration (transpiration divided by 

 evaporation) in the three beds was as follows: 



No shade 0.0633 2 



Half shade 0.0346 



Full shade 0.0088 



With these coefficients it is possible to calculate the transpira- 

 tion from the white pine seedlings from the evaporation from a 

 second set of black atmometers which had been running all 



2 In the report of the secretary of the Botanical Society given in Science New 

 Series No. 998 p. 259 some of these values were out of order. 



