58 



AGRONOMY 



the nucleus. The nucleus is the center of the cell's activities. 

 When a new cell is to be formed, the nucleus first divides 

 into two equal parts and then the division extends outward 



to the surrounding cell 

 wall. Soon there are 

 two new cells in place 

 of the original one, 

 new walls having been 

 constructed between 

 them. These two cells 

 now grow to maturity 

 and are ready to re- 

 peat the process. All 



growth is essentially like this. When growing alone, the cell 

 inclines to take a spherical shape, but in plant and animal tis- 

 sues, where it is crowded on all sides, it becomes more or less 



FIG. 30. Cells with nuclei from the epidermis 

 of the onion bulb 



Photograph by the United States Department of Agriculture 



FIG. 31. The root system of the corn plant 



angular. The cells in the woody parts of plants, in bark and 

 the like, are very different from the cell just described, but 

 all began as cells of this kind. 



