ROOTS 



221 



Fig. 90. A length- 

 wise section of a 

 carrot showing the 

 internal structure ; 

 E, epidermis ; C, 

 cortex ; and W, 

 woody part. 



some estimate of the amount of 

 water which enters the roots of 

 E plants each day. This absorption 

 of water takes place chiefly through 

 the root hairs. The soil water 

 contains all the sub- 

 stances which it can 

 dissolve from the 

 earth through which 

 it passes. This water 

 with these solutes 

 then diffuses through 

 the thin walls of the 

 root hairs. We have 

 already learned that 

 some liquids will dif- 

 fuse through an ani- 

 mal membrane even 

 though there are 110 

 in the membrane. In exactly i\& 

 as the molecules of molasses and 



(See 



.Root Cap 



Fig. 91. Radish 

 seedling grown 

 in moist air to 

 show the root 

 hairs. 



visible pores 

 same manner 



water diffused through the animal membrane 

 Exercise 5), the soil water and solutes pass through 

 the walls of the root hairs. From there they are con- 

 ducted through tubes up through the root into the stem. 

 Substances also pass out of the roots into the soil. 

 Movement takes place in both directions through the 

 walls of the root hairs. Those substances which pass 

 out of the root are waste products, excretions. 



