CHAPTER VII. 



THE GROWTH OF BOOTS AND STEMS. 



181. As we have seen, the green leaf makes organic food 

 from the raw materials which it takes from the air and from 

 the soil. It also serves as the chief means by which the 

 air within the plant communicates with the atmosphere, and 

 by which the gaseous exchanges concerned in respiration and 

 transpiration are carried on. These functions are also carried 

 on by the other green parts of plants, e.g. by young stems, 

 both in herbaceous and woody plants, since the rind (cortex) 

 contains chloroplasts, and the stomates (on herbaceous stems 

 and the youngest parts of woody stems) or lenticels (in older 

 parts of woody stems) communicate between the air-spaces 

 in the plant and the atmosphere outside. 



We have already learned something about the growth of 

 roots and shoots from our work on seedlings and on the 

 nutrition of the green plant. We may now take up the ques- 

 tions on the growth of root and shoot raised in Art. 104. 

 It is absolutely necessary to grasp thoroughly the main facts 

 in the nutrition of plants above all, the work of the green 

 leaf, which is the great fundamental process and which may 

 be said to form the key to the right understanding of the 

 structure and development of root and shoot and all the 

 varied forms and adaptations of the vegetative organs. 



* 182. How to measure the Growth in Length of Root 

 and Stem. Seedlings of Broad Bean, G-arden Pea, and 

 Scarlet Runner are suitable for experiments on the growth in 

 length of root and stem. Place the seeds in damp sawdust with 

 the scar downwards. Runner Beans are especially useful for 

 measurements of the growth of the stem. 



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