100 



BOTANY. 



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

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



eventually sepa- 



/ ! / VS 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- 



k 



circular forms, 

 and constitute the 

 guard-cells before 

 mentioned. The 

 details of the fore- 

 going process in 

 one of its more 

 complex forms 



Fig. 89. Stomata from the under surface of the leaf of * _ .. . 



Echi/tocystis lobata. , s. stomata ; g, g, irregular epider- are illustrated in 



mis-cells between the veins of the leaf ; v, elongated and -& M A AT) 



regular epidermis-cells over a vein. X 250. From a -Tig. "I? -d. ana Z>. 



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 

 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, 



Fig. 90. Double stomata from the under surface 

 of the leaf of Echinocystis lobata. X 500. From a 

 drawing by J. C. Arthur. 



