PLANT STRUCTURE 143 



material around the injured parts. This causes rapidity 

 of growth. Buds are formed and consequently many 

 young rootlets develop. Thus the feeding area of the 

 plantlet is increased many fold. As this occurs near the 

 base of the stem, the feeding root area is brought nearer 

 the leaf area, the stem becomes stocky and the foliage 

 dark green and healthful. Repotting plants which are 

 pot-bound accomplishes the same purpose. Therefore, 

 cuttings are placed in small pots which are frequently re- 

 placed by larger ones as the root system develops. If the 

 soil is generously supplied with plant food and moisture, 

 the roots will not be obliged to travel long distances in 

 search of them. Consequently the roots will be shorter, 

 while growth in diameter will increase proportionally. 



Roots are dependent on the oxygen of the air for the 

 healthy action of the root-hairs, therefore, it is essential 

 that the soil be well aerated. There should be the proper 

 relations between the soil-moisture contents and the air 

 spaces of the soil. Water-soaked soil becomes sour and 

 unsuited for alert growth. 



109. Correct moisture contents of the soil. The 

 amount of water required by actively growing plants is 

 considerable. The water is almost wholly absorbed by 

 root-hairs, as leaves have no power to take in water. 

 Healthful growth demands that at all times there be suffi- 

 cient moisture in the soil, so that the plant may get suffi- 

 cient food material in solution to nourish it. Growth 

 by cell division can take place only when the cell walls are 

 first distended with water. The strong affinity for water 

 which protoplasm possesses is largely responsible for the 

 expansion of plant tissue, such as the unfolding of leaf and 

 flower buds. The elastic cell walls of growing tissue are 

 distended until they are like minute, inflated bladders. 



