CH. IV] WITH ABSOEPTION. 91 



growing shoots, or remove any that may be present. Let 

 it remain in water for 24 hours, cut a fresh surface and 

 fit it in a bottle arranged as in the fig. 16. The branch 

 B fits a tube which pierces the cork and should dip well 

 into the water in the bottle. Through another hole in the 

 cork a tube T graduated into y^cc. and holding about 

 20 c.c. is passed : this serves to record the amount of 

 water absorbed by B : the opening of T must be closed 

 with a plug of cotton wool to allow air to enter, and yet 

 to hinder evaporation from T. In one experiment we 

 found that a branch of laurel with 30 leaves weighed, with 

 the bottle of water, 287 grams : by using one of Becker's 

 balances without a glass case, and having a beam sup- 

 ported 40 cm. above the table of the balance, it was 

 possible to place the bottle on the pan and arrange the 

 leaves and branches so as to be clear of the scale-pan 

 knife-edges. 



Weighings and readings should be taken at hourly 

 intervals. The burette ought to be read to O'Ol c.c, if the 

 weight is recorded to O'Ol gram. It is instructive to 

 repeat the experiment with a freshly cut branch in which 

 the negative pressure is not satisfied. It will be seen 

 that the absorption is much greater than the loss by 

 weight, it may, for instance, be three times as great. 

 After taking a few hourly readings the apparatus should 

 be left to itself for 12 hours when equality between gain 

 and loss should be fairly established. 



(116) Spring Balance. 



We have found the following arrangement, fig. 17, useful 



