HOW THE PLANT LIVES 



125 



plural is stomata or stomates. Fig. 38 shows a fragment of leaf 

 in cross -section, a being a stoma opening out on the lower sur- 

 face. Looking down upon the 

 peeled-off epidermis of the lower 

 surface, stomata are seen at Fig. 39. 

 188fe. Cut off a leafy branch of 

 any herb, insert the stem through 

 a perforated cork into a bottle of 

 water, and then place the whole 

 under a bell-glass. Note how soon 

 the water vapor thrown off condenses 

 upon the glass. Compare Fig. 10, 

 page 58. 



188c. The rate of tran- 

 spiration from a single leaf 

 may be accurately observed 

 as follows : A large U- 

 shaped glass tube is fillei 

 with water, and into one end 

 of this tube is inserted a 

 perforated cork bearing a 

 small glass tube or capillary 

 arm, bent at right angles. 

 In the other end of the U- 

 tube is fitted a cork, through 

 the perforation in which is 



inserted the leaf-stalk, with the stem reaching 

 the water, as shown in Fig. 40. When this last 

 cork is forced in, water will fill the capillary arm; 

 and the recession of the water in this arm to 

 supply that transpired shows the rate of tran- 

 spiration. Wax or paraffin should be used to seal 

 around the perforations. 



189a. Root -pressure or sap-pressure, may be 



made evident roughly by a very simple experiment. 



, _ Fig. 87. How the 



An inch or so above ground, cut off a stem of some goil a( jhere to 



actively-growing herbaceous plant, as the sun- the young root. 



Fig. 36. The root-hairs 

 as seen on a dark, 

 damp cloth. 



