254 



LEAF-ANATOMV OF SCEVOI.A CRASSIFOLIA, 



allel to the pore. In S crassifolia there are no subsidiary cells. 

 A single epidermal cell divides by an oblique wall into two cells 

 of unequal size. The larger of these cells remains an epidermal 

 cell, while the smaller is the mother-cell of the guard-cells. The 

 only further division which takes place is that which forms the 

 two guard-cells. The mature stoma is surrounded by a variable 

 number of epidermal cells ( Text. fig. 4 o?). The stomata reach 



Text-fig. 4. — Stages {a-c) in the development of the stomata, as seen in 

 transverse section of young leaf : a, initial stage, showing mother- 

 cell of the guard-cells; Ji-r, showing development of two guard-cells; 

 no pore is formed; d, sui'f ace-view of young leaf, showing stages 

 in development of stomata; ( x 300). 

 their full development when the flow of secretion has ceased. 

 Those which mature first, are lendered functionless, for a time 

 at least, owing to the blocking of their pores with resin. It 

 seems highly probable that many of those stomata, in which a 

 plug of resin is found enclosed in the stomatal aperture, will 

 never function (PI. xxviii., fig. 4). Only those stomata which 

 are belated in development, and are freed before reaching matu- 

 rity, by the drying-up and cracking of the resin, are entirely 

 unblocked by the secretion. 



In those plants with lacquered leaves, which Yolkens(6) de- 



