40 



PLANTS 



this chlorophyll which gives green plants their characteristic 

 color. It may be extracted from green tissues by alcohol, in 

 which it is soluble, the alcohol then becoming green and the 

 chloroplasts colorless. 



83. The function of the various parts of the leaf may be 

 determined by suitably conducted, simple experiments. 



84. The usual position of the stomata, on the underside of the 

 leaf, indicates that the stomata are not organs for the absorption 



Fig. 16. — Stereogram of leaf structure. Part of a veinlet is shown on the right. 

 Intercellular spaces are shaded. (From Stevens.) 



of water. Besides, most leaves, due to the presence of a waxy 

 secretion on the surface of the epidermis, do not wet and, con- 

 sequently, water w^ould not pass through the minute openings. 

 The function of the stomata must be to permit an interchange 

 of vapors and gases between the intercellular air spaces and the 

 atmosphere; for by experiment it can be shown that water vapor 



