ROOTS. 



91 



absorb moisture from them. By these root hairs the absorb- 

 ing surface, and hence the amount of absorption, is greatly 



increased. Individual 

 root hairs do not last 

 very long, but new 

 ones are constantly ap- 

 pearing just behind the 

 advancing root tips, 

 and the old ones are 

 as constantly disap- 

 pearing. 



(1) Oeot7-opism and 

 'hydrotropism. — Many 

 outside influences afPect 

 roots in the direction 

 of their growth, and 

 as soil roots are espe- 

 cially favorable for ob- 

 serving these influ- 



FiG. 85. Apparatus to show the influence of 

 water (hydrotropism) upon the direction of 

 roots. The ends (a) of the box have hooks 

 for hanging, while the box proper is a qylinder 

 or trough of wire netting and is filled with 

 damp sawdust. In the sawdust arc planted 

 peas (g-), whose roots (/i, i, k, m) first descend 

 until they emerge from the damp sawdust, 

 but soon turn back toward it. — After Sachs. 



ences, two prominent 

 ones may be mentioned. The influence of gravity, or the 

 earth influence, is very strong in directing the soil root. 



Fig. 86. A raspberry plant, whose stem has been bent down to the soil and has " struck 

 root." — After Beal. 



