100 



BOTANY. 



■the mother-cell is formed a median partition- wall forms 



in it, and gradually becomes separated into two plates, which 



eventually sepa- 

 rate and form a 

 pore through 

 the epidermis. 

 The two halves of 

 the mother-cell be- 

 come symmetrical- 

 ly rounded off into 

 semilunar or semi- 

 circular forms, 

 and constitute the 

 guard-cells before 

 mentioned. The 

 details of the fore- 

 going process in 

 one of its more 

 complex forms 

 are illustrated in 

 Fig. 91, A and B. 

 The splitting of 



the middle partition-wall of the mother-cell is shown in the 



successive sections (Fig. 92). 



132. — In the light, under certain conditions of moisture 



and temperature, the 



Fig. 89. — Stomata from the under surface of the leaf of 

 Echmoaystis Mala. «, s, stomata ; g, g, irregular epider- 

 mis-celle between the veins of the leaf'; «, elongated and 

 regular epidermis-cells over a vela. X 250.— From a 

 drawing hy J. C. Arthur. 



ii^^l 



guard-cells become 

 curved away from each 

 other in their central 

 portions, thus opening 

 the slit and allowing 

 free communication 

 between the external 

 air and that in the in- 

 tercellular spaces and 

 passages of the leaf. 



(a) A superficial examination of stomata may be easily made by 

 stripping off the epidermis, and mounting it in water or alcohol. Good 

 sections of stomata are more difficult to make ; they may be obtained, 



Kg. 90.— Double stomata from the under surface 

 of the leaf of Echinoeystis Idbata. x 5D0.— Prom a 

 drawing by J. C, Arthur. 



