124 



ROOTS AND UNDERGROUND STEMS 



262 



- Root of a tree on the side of a guUey 

 acting as stem. 



your specimen, continuing it an inch or two into the stem ; 

 do you find any sharp line of division between the two ? 



175. The Active Part of the Root. — It is only the newest 

 and most delicate parts of the root that produce hairs and 



are engaged in the active 

 work of absorption, the 

 older parts acting mainly 

 as carriers. Hence, old 

 roots lose much of their 

 characteristic structure 

 and take on more and 

 more of the office of the 

 stem, until there is prac- 

 tically no difference be- 

 tween them. On the 

 sides of gullies, where 

 the earth has been 

 washed from around the 

 trees, we often see the 



upper portion of the root covered with a thick bark and 



fulfilling every office of a true stem. 



176. Use of the Epidermis. — Cut away the lower end of 

 a taproot ; seal the cut surface with wax so as to make it 

 perfectly water-tight, and insert it in red ink for at least 

 half the remaining length, taking care that there is no 

 break in the epidermis. Cut an inch or two from the tip 

 of the lower piece, or if material is abundant, from another 

 root of the same kind, and insert it without sealing the cut 

 surface, in red ink, beside the other. At the end of three 

 or four hours, examine longitudinal sections of both pieces. 

 Has the liquid been absorbed equally by both ? If not, in 

 which has it been absorbed most freely .■" What conclusion 

 would you draw from this, as to the passage of liquids 

 through the epidermis .' 



From this experiment we see that the epidermis, besides 

 protecting the more delicate parts within from mechanical 

 injury by hard substances contained in the soil, serves b.v 



