HOW THE PLANT LIVES 121 



the plant is composed, new cells are made, and 

 others are modified in size or form. It is prob- 

 ably impossible for a plant to live without grow- 

 ing ; but under poor conditions the growth may be 

 so slight that the plant is no longer of any use 

 to the farmer. 



205. The young stems of many plants elongate 

 throughout the entire length of the growing 

 part. But the lower part soon reaches the limit 

 of its growth, the rear internode or space be- 

 tween the joints ceases to elongate, and further 

 growth in length proceeds only in the newer parts 

 above. That is, while there is an elongation or 

 stretching of the shoot itself, this elongation 

 gradually lessens below, so that the region of 

 most rapid growth is constantly in the freshest 

 and softest part of the shoot. Notice that the 

 distance between the joints in growing shoots 

 tends for a time to increase. 



206. The root grows differently. The tip of 

 the growing root is hard, being protected by what 

 is known as a root -cap. Growth in length takes 

 place just behind this hard tip, not throughout 

 the length of the growing part. The root, there- 

 fore, is able to push its way around obstacles. 



207. In most of our woody plants, increase in 

 diameter is effected by a layer of growing tissue, 

 the cambium, located just beneath the bark; and 

 every year it gives rise to a new layer of wood ou 



