240 HOW CROPS GROW. 



strated by placing the old, brown-colored roots of a plant 

 in water, but keeping the delicate and unindurated ex- 

 tremities above the liquid. Thus situated, the plant with- 

 ers nearly as soon as if its root-surface were all exposed to 

 the air. 



1). Its Rapid Extension in Length, and the vast Sur- 

 face which it puts in contact with the soil, further adapts 

 the root to the work of collecting food. The length of 

 roots in a direct line from the point of their origin is not, in- 

 deed, a criterion by which to judge of the efficiency where- 

 with the plant to which they belong is nourished; for 

 two plants may be equally flourishing be equally fed by 

 their roots when these organs, in one case, reach but one 

 foot, and in the other extend two feet from the stem to 

 which they are attached. In one case, the roots would be 

 fewer and longer ; in the other, shorter and more numer- 

 ous. Their aggregate length, or, more correctly, the ag- 

 gregate absorbing surface, would be nearly the same in 

 both. 



The Medium in Which Roots Grow has a great influence 

 on their extension. When they are situated in concen- 

 trated solutions, or in a very fertile soil, they are short, 

 and numerously branched. Where their food is sparse, 

 they are attenuated, and bear a comparatively small num- 

 ber of rootlets. Illustrations of the former condition are 

 often seen. Bones and masses of manure are not infre- 

 quently found, completely covered and penetrated by a 

 fleece of stout roots. On the other hand, the roots which 

 grow in poor, sandy soils, are very long and slender. 



Nobbe has described some experiments which com- 

 pletely establish the point under notice. ( Vs. St., IV, p. 

 212.) He allowed maize to grow in a poor clay soil, con- 

 tained in glass cylinders, each vessel having in it a quan- 

 tity of a fertilizing mixture disposed in some peculiar man- 

 ner for the purpose of observing its influence on the roots. 

 When the plants had been nearly four months in growth, 



