ROOTS 



19 



the plant through root hairs, which are found near the tips of 

 the smallest rootlets. In reality, the root hairs are the ab- 

 sorbing organs of a plant. When we pull up any common 

 herbaceous plant, we observe, as a rule, a large number of 

 hair-like rootlets as branches of larger roots. These fine 

 "hair roots" are sometimes mistaken for root 

 hairs. But, closer examination, in which a 

 hand lens may be necessary, shows us that 

 these hair roots are the bearers of root hairs. 

 In fact, root hairs are found only on the 

 smallest and youngest rootlets. 



Root-hair Zone. — Root hairs do not grow 

 along the full length of a rootlet, but occupy 

 a definite zone, designated the root-hair zone. 

 This is clearly seen in young seedlings, 

 grown on moist filter paper. The root- 

 hair zone appears as a white fuzzy coating. 

 The root cap is free of root hairs. The 

 length of the zone varies from a few milli- 

 meters to several centimeters. The root- 

 hair zone of seedlings grown in soil is plainly 

 evident from the mass of soil particles held 

 by the root hairs (Fig. 8). Each root hair 

 in its growth flattens out over, and some- 

 times partially surrounds, the soil particles 

 with which it comes into contact, thereby 

 forming a close connection with the water 

 and solutes that form a thin film around 

 each soil particle (Fig. 9). Furthermore, the root hairs 

 become mucilaginous, and this, along with their partial sur- 

 rounding of particles, explains the presence of the mass of 

 soil particles that clings to rootlets in the root-hair zone. 

 Root hairs are short-lived, persisting for only a few days or 



Fig. 8.— Wheat 

 seedling showing 

 soil particles cling- 

 ing to root hairs; 

 note that the root 

 cap is free of root 

 hairs. 



