102 PRACTICAL BOTANY 



IV. Transverse sections should also be cut from the foliage- 

 leaves of the Hyacinth, which, as above noted, grow in an 

 almost vertical position : mount in glycerine, and note under a 

 low power that there is no great difference between the upper 

 and lower surfaces as regards the disposition of the tissues, 

 excepting that the orientation of the collateral bundles is such 

 that the xylem is directed towards the upper surface. 



Stomata may be seen both on the lower and upper surfaces : 

 there is no distinctly marked palisade-parenchyma : centrally 

 is a mass of colourless thin-walled parenchyma. Note the 

 absence of strengthening sclerenchyma. 



This will be found an excellent opportunity for the study of 

 the details of a simple stoma: observe that the guard-cells 

 are about at the general level of the epidermis : that when 

 fairly cut through the middle they differ in section from the 

 other epidermal cells : the cell-wall separating them from the 

 adjoining epidermal cells is relatively thin, while that adjoining 

 the pore of the stoma is thick, excepting at one point, where 

 the guard-cells are near to, or in contact with, one another. 

 There are external and internal thickened ridges on each 

 guard-cell, which appear in section as sharp projecting teeth : 

 these respectively define and partially inclose the front cavity 

 and back cavity of the pore. The cuticle is seen to be con- 

 tinuous through the pore, to the lower surface of the epidermis. 

 Note also the large air-chamber leading into the system of 

 intercellular spaces of the cortex. The contents of the guard- 

 cells are conspicuously stained blue with chlor-zinc-iodine. 



V. To observe the stoma in surface view, and in the living 

 condition, take leaves of Hyacinth, or better of some species 

 of Lilium, in which the stomata are of unusually large size : on 

 a bright day, and after full exposure to the light, strip off a 

 piece of the epidermis : mount it in water, with the outer 

 surface uppermost, and examine under a low power. It may 

 then be readily seen that the pores of the stomata are widely 

 open, the guard-cells being strongly curved. 



Having seen this, irrigate with a 2 per cent, solution of 

 common salt, keeping watch upon a stoma which has been seen 

 to be open : when the salt solution reaches it, the stoma will 



