Anderson: growth of cucurbita. 241 



A record was kept of the temperature and relative humidity 

 by means of dry and wet bulb thermometers. The method 

 followed was that of the U. S. Signal Service. Tables of this 

 institution were also used in the determination of the relative 

 humidity. ^ 



A record was also kept of the barometric pressure. A. second 

 registering balance was used from time to time for determining 

 the rate of transpiration of the leaves and for taking the de- 

 crease of fruit no. 2. For measuring the rate and amount of 

 transpiration of the leaves and internodes this balance was set 

 up as previously described.^ A branch of the same vine bearing 

 the fruit on the first registering balance, was taken through an 

 aperture in the sash of another window. The second register- 

 ing balance had previously been arranged and placed near this 

 window. 



A portion of the tip of this branch, 35 cm, in length bearing 

 five small leaves was extended through a piece of rubber cloth 

 tied and sealed to the bottom of an 8 liter bell glass. The aper- 

 ture in the rubber cloth was sealed and all connections with 

 the open air and absorber were the same as figured in a XDre- 

 vious number of this bulletin. " 



An aspirator was connected with the city water supply, the 

 pressure of which varied somewhat from time to time. This 

 variation, however, could be guarded against since the aspira- 

 tor had an index and could be regulated. By keeping an equal 

 flow of water a constant current of dried air could be drawn 

 through the bell glass containing a part of the Cucurbita vine 

 and leaves. In the arrangement of an absorber in the transpir 

 ation chamber, it was found after repeated experiments that 

 calcium chloride alone would not take up all the moisture from a 

 current of air passing rapidly through it. When the per cent, of 

 moisture was small the error was slight and inappreciable, but 

 when transpiration was rapid and it was necessary that the air in 

 the bell glass should be entirely renewed every five minutes, 

 the calcium chloride soon lost its power of absorption and 

 some of the water passed through. This error was guarded 

 against by using an absorber charged with calcium chloride 

 and sulphuric acid in separate vessels.*^ The absorber con- 

 sists essentially of two low flasks. The first one, containing 

 about 20 c. c. of concentrated sulphuric acid receives the cur- 



5. Signal Service, War Dept., Auiiuul Key. 27?, 301, :i03, 1886. 



I). Minn. Bot. ytud. Pt. 4. 1"1». 1894. 



7. Plate VII. Miuii. Boi. Stud. Pt. 4. 222. 181)1. 



S. Minn. Bot. Stud. pt. 4. 179. 18i)». 



