XEROPHYTES AND HALOPHYTES. 



241 



Stalk of sugar-cane (fig. 204). The interior layers of the 

 wall of the epidermis are sometimes converted into mucilage, 

 which retards the evaporation of water. 

 The sinking of the stomata below the 

 general level (fig. 205), their arrangement 

 in pits (fig. 206) or in grooves (fig. 197), 

 and their restriction to the under side of 

 the leaf (fig. 206) may- 

 be looked upon as 

 further epidermal 

 adaptations to reduce 

 evaporation. In the 

 leaves of some xero- 

 phytes the guard cells 

 of the stomata are 

 only when 

 young, becoming 

 thick-walled and fixed when the leaf is mature. The stoma 

 itself sometimes becomes closed, also. fh) The internal 



Fig. 203. — Shieldlike scales of an Q\&d&X^x{EliBagnus 

 angustifolia). seen from ■above. Magnified about mr»fil<a 

 SO diam.— After Kemer. muuie 



--,et 



Fig 204. Fig 205. 



Fig. 204. — Portion of a transverse section through a node of sugar-cane, showing rods 

 of wax secreted by the epidermis. Magnified 142 diam. After De Bary. 



Fig. 205.— Transverse section of a portion of the margin of a leaf of Aloe socoirina. 

 <r, thick cuticle; <u, cutinized layers of wall of epidermis, ep\ p, green cells; cr, 

 a crystal cell with needle crystals of oxalate of lime ; j/4, guard cells of stoma, 

 sunk below surface ; a, intercellular space under stoma. Magnified about 175 diam. — 

 After Tschirch. 



