132 



BOTANY: PRINCIPLES AND PROBLEMS 



a certain point, it poisons the yeast plant and fermentation 

 ceases. 



The respiration of other minute plants may also bring about 

 alcoholic fermentation, and still others produce fermentations 



^^ ^)>AbsorpHon 



Growth 



Fig. 68. — Important structures and functions of the plant. Diagrammatic 

 representation of roots, stem, leaves, and buds and their functions. Wood solid 

 black, bast dotted, pith and cortex white. Arrows indicate movement of mate- 

 rials into the plant, along the stem, and to and from the leaves. One leaf repre- 

 sented in section. Water passes from the root upward to stem and leaves, 

 through the wood. Manufactured food passes from the leaves both upward 

 and downward, through the bast. The various gas-exchanges between leaf and 

 atmosphere are graphically represented. 



