354 



Transactions. 



Stomata. — vStomata are numerous on the ventral surface, but absent 

 on the dorsal. Development, as far as I have made out, takes place in 

 the usual way, and the first stomata are formed about the 4th leaf from 

 the apex. The guard-cells are long, and are comparatively narrow. Their 

 walls are thick, and at the top and bottom the thickened portion of the 

 wall bounding the pore projects in the form of a ridge. Midway between 

 these ridges the walls are not thickened, and when turgid jut out into the 

 pore, and thus facilitate its closing. The guard-cells are half the epidermal 

 cells in height, and are sunk beneath the epidermis, the inner walls being 

 in the same plane as the inner walls of the epidermal cells. 



Warming (2) and Miss Cross (7) describe stomata as not being sunk. 

 [ found that they were sunk in every case, except in the cotyledons, which 

 are not referred to by either of these writers. 



Stoma 



Respiratory cavity 



Aqueous 

 tissue 



Scattered 

 tracheide 



Aqueous tissue 



Stele Aoueous tissue Chhrenchyma 



Fibro-vascular 

 bundle 



Epidermis . 



Aqueous tissue 



DTO 



Fig. 4. — a, Transverse section of stem surrounded by leaf and leaf-bases; b, trans- 

 verse section of tracheides; c, longitudinal section of stoma at 9.30 a.m.; 

 d, longitudinal section of stoma at 6 p.m. ; e, transverse section of epidermis 

 of cotyledon, showing cells dividing. 



If a longitudinal section of leaf or leaf-base is taken at the end of the 

 day, after transpiration has been going on freely, it is seen that the cells 

 which abut on the guard-cells curve over them. If a section is taken late 

 that night or early the next morning, these cells are no longer curved. Thus 

 when turgidity is reduced the cells curve over the stoma, and the amount 

 of transpiration is diminished (see fig. 4, c, d). 



The stomata are situated above the palisade tissue. This is not usual 

 in ordinary leaves, but occurs in plants having much the same structure 

 as Salicornia. The guard-cells are at right angles to the axis of the 

 stem. 



