EVERGREEN TREES IN WINTER. 317 



A. — 3Ieihod of determining the amount of water transpired by 

 plants, by iveighing. The first method, recommended by many 

 investigators as being the most accurate for experiments in which, 

 of course, rooted plants must be employed, was fully discussed 

 by Burgers te in^\ A number of evergreen trees, 40-60 cm. high, 

 were selected for my experiments and planted last September in 

 pots, measuring 15 cm. in diameter and 12 cm. in height. These 

 pots in which the plants grew were enclosed within metallic cases 

 of exactly the same form and size, and having bisected covers. 

 For cementing the covers hermetically, I used tin-foil and a 

 mixture of beeswax and olive oil. Through the covers a hole for 

 supplying water was made which, however, was closed air-tight 

 during the experiments. The whole weight of each pot, including 

 the plant and the cover, amounted to about 2 kgr., when the 

 soil contained in it was saturated with water, and I knew by 

 calculation that about one third of the whole weight represented 

 the quantity of water contained in the soil. By this method, I 

 Avas able to make a rough estimate of the amount of water con- 

 tained in the soil at different times during the experiments. 



Since the activity of the root is weakened in a closed soil 

 owing to the deficiency of the air supply '\ experiments of long 

 duration must be avoided. During the experiments I opened 

 the hole in the cover several times, in order to supply water 

 and also to renew the air. 



B. — IletJiod of oneasuriîig the amount of luater transpired by 

 p)la7its, by absorption. The apparatus which I employed for 

 measuring absorption was a slight modification of the potometer 



1) Burgersteiii, Materialien zu einer Monographie betrellend die Erscheinungen der 

 Transpiration der I'llanzen 1889, II, p. 5. 



2) Sachs, Vorlesungen über PflanzenpliVbiologie 1882, p. 307. 



