X] EXCRETION OF WATER 107 



pressed through the pores, and the watery vapour es- 

 caping from ordinary stomata, is that the former carries 

 dissolved salts and other substances with it. In many 

 cases large quantities of lime are held dissolved in the 

 carbonic acid with which such water abounds, and on the 

 escape of the gas and the evaporation of some of the 

 water, carbonate of lime in some quantity accumulates at 

 the teeth and other points where the water-pores exist. 

 Such accumulations of chalk are characteristic of many 

 Saxifrages e.g. Saadfraga crustata, S. Aizoon, &c. and 

 are to be seen on the teeth of old leaves of Salix fragilis, 

 &c. 



It is not improbable that the water-stomata in bud- 

 scales also act as relief to pressure ; while in young leaves 

 breaking through the bud the marginal teeth may begin 

 their action very early, e.g. species of Primus, Platanus,&c. 



