MAIZE. LEAF. 117 



Treat with acetic acid no evolution of gas. 



Treat with nitric acid it is not dissolved. 



The residue is a silica-skeleton of the epidermal 

 tissues. 



VI. Development of Stomata. Take a young leaf 

 from a bulb of Hyacinthus orientalis in which the leaves 

 have not yet protruded more than about one inch from 

 the apex of the bulb. Strip off pieces of the epi- 

 dermis (or cut tangential sections at successive points) 

 starting from the apex, and proceeding to the very 

 base. Mount in glycerine, and examine under a high 

 power. 



i. Starting at the basal part, cell-division will be 

 found to be proceeding actively in the epidermal tissue ; 

 the walls are thin, and protoplasm copious. The 

 epidermis consists of 



a. Larger oblong cells. 



b. Short, nearly square cells. 



The cells are arranged in regular longitudinal rows. 



ii. At a short distance from the base, the difference 

 in size of (#) and (5) increases ; some of the square cells 

 may be seen to be divided by a thin longitudinal wall, 

 into two equal halves (guard-cells of the stoma). 



iii. Further up again, this division wall may be seen 

 to be thicker at its central part, while the whole outline 

 of the pair of guard-cells tends to become circular. 



iv. Again further up, the division wall will be seen to 

 have split, so that a channel is formed between the 

 guard-cells into the internal tissues of the leaf. This 

 channel is the pore of the stoma. 



v. Near the apex of the leaf the mature stomata may 

 be seen of circular outline ; their guard-cells are sausage- 



