THE WORK OF LEAVES 



205 



melt and run off if it is too thickly smeared on ; for 

 this reason grafting- wax is better.) 



In examining the epidermis of leaves under the 

 microscope, we find the stomata sometimes open and 

 sometimes closed, as in Fig. 

 113. Since, as we have already 

 found, all, or nearly all the 

 water passes out through the 

 stomata, we may judge whether 

 they are open or closed by the 

 amount of water the leaf gives 

 off. This may be measured by 

 the methods just described or 

 by means of the apparatus 

 shown in Fig. 119. A leaf is 

 removed from the plant and 

 slipped into a cork borer 

 (just large enough to re- 

 ceive it) , which has beei} 

 previously forced through 

 a rubber stopper, as 

 shown in Fig. 118. On 

 withdrawing the cork 

 borer, the leaf will be found firmly fixed in the rubber 

 stopper. In this way a leaf or a stem may be quickly 

 fixed air-tight in such a stopper without injury. A 

 piece of small glass tubing, about fourteen inches 

 long (the smaller the bore the better) , bent as shown 



118. Method of inserting a leaf-stalk 

 air-tight in a rubber stopper. 



