34 BOTANY 



be recognised in the zone of cell division. The cells of 

 these layers can divide and they are called in conse- 

 quence meristematic layers. The outermost, which is 

 known as the dermatogen, forms the root cap, and ex- 

 tending backwards gives rise also to the outermost 

 layer of the root from which the root hairs grow. The 

 central one forms a more or less well-marked cylinder 

 or core, which is known in the meristematic region as 

 the plerome, while the intermediate one is called the 

 periblem, and forms the part of the root that lies 

 between the central cylinder and the external layer. As 

 we trace these further backwards we find that the 

 central cylinder becomes very clearly marked off from 

 the rest by a peculiar layer called the endodermis. 



The root hairs are long slender outgrowths of the cells 

 of the outer layer, which when past the meristematic 

 region is known as the pili/erous layer, or epiblema. 

 Each hair has a thin wall of cellulose, which is brought 

 into close contact with particles of soil as it grows in 

 among them. On coming into contact with these 

 particles the outer layers of its walls become changed 

 into a kind of mucilage, which makes the hair adhere 

 very closely to the soil. The film of water which sur- 

 rounds the particles is then absorbed by the root hair. 

 As there are enormous numbers of these hairs on the 

 young root, there is soon a great increase in the water 

 which the root contains. This water passes on from 

 the hairs into the second region of the root, now called 

 cortex instead of periblem, and gradually makes its cells 

 extremely swollen or turgid thereby. 



The special mechanism for carrying this water 

 from the root to the upper parts of the plant is by this 

 time beginning to appear. It lies in the central region, 

 now partly shut off from the rest by the endodermis. 

 Here the growth of the cells is such as to cause them 

 to become elongated. Certain special areas of these 



