How rm: i-lan'T LIVES ll") 



ptotnata, are especially abuiidaut on tlie uiuler 

 surfaeos of most leaves. With changes in the 

 water content of the plant, these stoniata open 

 or close, to a dej^reo fai-ilitating or inhibitinj^: 

 transjiiration. Like evajmration, tianspiration is 

 hastt'iit'd by higher tenipcralinvs, dry air, wind, 

 and the movements of the plant. On a very 

 hot day, or with insullicient soil moisture, a 

 plant may wilt, due to the fact that all of the 

 facilities for cheeking transjiiration fail to keep 

 the lialance betwiMMi root absorption and tian- 

 spiration. Th«> jdaiit gives off more water than 

 it tak»'s up; therefore, it wilts. 



18!). The absorptive activity of the roots gives 

 rise to a sap- or root -pressure which tends to 

 force tho current upward. In fact, the lifting 

 powor of transpiration, <^smosis, root-pressure, 

 and otht'r forces cause tln> crude sap to ascend 

 through th»> woody bundles of the plant; and by 

 in«'ans of these bundles absorbed solutions are 

 <'arri«Ml upward thi-ough all parts of root and 

 stom, and tiirough the leaf-stalk, veins and vrin- 

 lets to all parts of th»' l«'af. 



26. Soluble salts from fht' soil 



190. Along with the soil water absor})ed l)y 

 the roots, minute quantities of the various min- 

 eral salts necessary for plant growth aro tnk»'n 

 in. Thos«' salts are in solution. In tin' ]>Iant, 



