No. 469] 



BIO war OF CACTI 



43 



consequence. The important fact was cstalili>li('<l that the plant 

 does transpire measurable amounts of water even in the driest 

 times and that it absorbs water quite out of |)n)p(iriioii to its rate 

 of transpiration. 



of the plant but which has hitherto received little emphasis, 

 namely, to the role which the leaves plav in transpiration. 



On August 18 the ])()l_vnieter apj)aratn> (("aiuion, idoa. Fiir. 4) 

 was adjusted to take the transpiration of a brancli of the cac-tus 

 which bore leaves and which wa- >ituaie(l a few meter- north of 

 the laboratory building. The data derived from tin- experiment 

 are as follows: — 



Experimrni 4. Trau.^ 



The branch transpired at the rate of 234 milligrams in 

 hour, or 0.91 millii,n-ains per minute for 100 sq. cm. of trans 

 ing surface. 



As soon as the experiment was finished tlu> sm-face to the s 

 was coated with vaseline and tlic experiment wa- repeated, 

 following, therefore, is the transpiration of the leaves only. 



2:52p.m. 52.0 



The rate per lionr foi 



The surface of the >tt 

 that of the leaves at 97 



