100 



BOTANY. 



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

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



eTcntually 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 



Pig. 89.— Storaata from the under surface of the leaf of ^. j. ; j ■ 



Bchmoaystis lobata. s, s, Btomata ; g, g, irregular epider- are illustrated in 



inis-cell3 between the veins of the leaf ;», efongated and ^ri- oi * AT) 



regular epideimis-cells over 4 vein. X 350.— From a r Ig. yi, J£ aUU. Jj, 



drawing by J. C.Arthur. rpj^^ 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 diflBcult to make ; they may be obtained, 



U^[ 



Fig. 90.— Double st^miata from the under surface 

 of the leaf of Echirweystis lobata. X 500.— From a 

 drawing by J. C. Arthur. 



