194 



FLOWER-LAND. 



influenced by the light to which it is exposed, as well as 

 by the dryness or dampness of the atmosphere. 

 Through the stomates transpiration can readily take 

 place, and it is often very considerable. It has been 

 calculated that a common sunflower, 3^ feet high, 

 will give off a quart of fluid in a single day. 



I dare say you have noticed the leaves drooping 

 upon transplanted plants, and that in times of heat 

 and drought some plants begin to droop much sooner 

 than others. These are caused by the transpira- 

 tion of fluid through the leaves more quickly than 

 a fresh supply can be taken up through the roots. 

 You will perhaps understand the action of the 



stomata better if 

 you look at Fig. 

 J 7 1. There you 

 can see what the 

 substance or 

 thickness of a 

 beech leaf is like. 

 It is cut in two, 

 and held so that 

 you look at the 



Fig. 171. Transverse section of a beech leaf cu |- ec jcre very 

 (magnified 350 times) ; co, epidermis of upper 



surface; eu, epidermis of under surface; pa, much magnified, 

 parenchyma ; st>, parenchyma with cavities ; 



j, a stoma. You see how the 



stomate opens into a space or air cavity, and so the 

 surrounding cells of the parenchyma are open to the 

 atmosphere, and transpiration can easily take place. 



