PLANT GROWTH AT DIFFERENT STAGES 253 



the dry matter of the plant. The roots contain the 

 largest amount of fiber and the smallest amount of fat of 

 any part of the plant. Of the ash elements, soda is 

 present in greater amounts than in parts above the ground. 

 In the early stages of growth, the roots are very rich in 

 iron, which decreases as the plant matures, because of its 

 being given over to other parts. The nitrogen in the 

 roots never, at any stage of growth, exceeds 1.25 per 

 cent, of the dry matter. It is transported to the parts 

 above ground more rapidly than any other element. 

 During the last fifteen days of growth, there is but little 

 mineral food, except magnesia, taken up, and there is a 

 loss of about 12 per cent, of potash from the roots which 

 indicates that the retrograde movement of potash at 

 maturity may extend from the roots back to the soil. In 

 the later stages of growth, there is a great influx of mag- 

 nesia. Silica and the non-essential ash elements make 

 up the larger portion of the ash elements in the mature 

 plant. 



355. Stalk. The stalk, during growth, undergoes a 

 decided change in composition ; there is a gradual in- 

 crease in the content of fiber and a decrease in proteids. 

 The outside of the stalk has a different chemical com- 

 position from the pith. The largest per cent, of dry 

 matter is found in the stalks from two to three weeks 

 before maturity. As the plant matures, the proteid and 

 circulatory carbohydrates are transferred to the 'seed. 

 When mature, both the pith and stalk have a low protein, 

 fat and digestible carbohydrate content, and hence a low 

 feeding value. The pith is somewhat richer in nitroge- 



