the growth of the plant 91 



The Growth of the Plant 



The above discussion of soil improvement must 

 be considered in connection with a brief considera- 

 tion of how plants grow. The study of the life 

 processes of plants is the subject-matter of that most 

 interesting and important science, vegetable physi- 

 ology. A knowledge of its principles is of funda- 

 mental importance for the farmer, since agriculture 

 is after all only the practical application of vegeta- 

 ble physiology and soil physics. At this place only 

 the barest outlines of the facts connected with the 

 growth of plants can be attempted. 



Within each seed is wrapped up a tiny rudimen- 

 tary plantlet called the embryo. This consists of 

 one or more seed leaves, the cotyledons, a minute 

 bud or growing point called the plumule, and the 

 radicle or rudimentary rootlet. There is also a 

 greater or less amount of rich food material that has 

 been stored either in the thickened seed leaves or in 

 an enveloping layer called the endosperm. It is this 

 stored food material that gives many seeds such great 

 value as food for men and animals. Under favor- 

 able conditions of heat and moisture the young 

 plantlet begins to grow. The seeds swell, the seed 

 coats are ruptured, and the young plant emerges. 

 This process is called germination. While it is in 

 progress, the stored food material becomes soluble 

 and is used to nourish the young plantlet as it 

 pushes its first leaves up into tlie light and the ad- 

 vancing root tip is burrowing even more rapidly into 

 the soil. If this rootlet is carefully examined, it will 

 be seen that for a considerable space just behind the 



