HYACINTH LEAF 177 



cells straightening themselves as their internal tension 

 is relieved, and finally becoming plasmolysed. The con- 

 nection between the opening of the stoma and the 

 internal tension of the guard-cells is thus demon- 

 strated. 



It will not be amiss at this point to study the development 

 of the stoma. 



Take a young leaf or young scape from a bulb of Eyacinthus 

 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 

 epidermis (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 parts taken from points nearest the base, 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. 



&. 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 

 (a) and (&) 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-shaped, and 

 surround the nearly circular pore. The cells of the epidermis 

 remain oblong as before. 



If the sections be carefully stained with Kleinenberg's 



N 



