How Plants Grow 39 



tudc of these little units. The food is made within 

 the cells, and oxygen is used within the cells. It is the 

 cells that need water, and it is the cells that are alive and 

 grow. 



How a plant grows. Plants grow in two ways : the 

 cells multiply, and they increase in size. 



When a cell divides, the nucleus first separates into 

 two parts. Then a wall or partition grows across the cell. 

 Thus two cells are formed where there was but one 

 before. In the tips of growing stems and roots, where the 

 growth is active, the cells are dividing very rapidly, 

 and this multiplication of cells causes growth in these 

 parts. 



In older parts of the plant, growth is largely due to 

 the increase in the size of the cells. This enlargement of 

 the cells is caused chiefly by the taking in of water, 

 which collects within the cell. After a warm rain in 

 early summer, the young corn plants take in water and 

 the cells expand so rapidly that sometimes the amount of 

 growth in a single night is noticeable. In the older re- 

 gions of the root or stem a cell often has a volume one 

 thousand times as great as the volume of one of the young 

 .cells in the growing tips. As the cell enlarges, its wall 

 stretches, and new materials are formed in it, so it in- 

 creases in size with the rest of the cell. 



How new parts are formed. If we could see the plant 

 at the very beginning of its life, we would find that it 

 consists of. just one cell within the young seed. This cell 

 divides and multiplies and soon develops into the embryo 

 or tiny plantlet which we find within a seed. The root 

 which pushes out when the seed germinates is formed 



