I0J5 



iiidiciite (liree possible levels al which the sloma may be eiit in 

 seelioiis parallel to the surface; (he lines d and e indicate two 

 possible ways in which in a transverse section through the leaf a 

 razor directed more or less parallel to the slit opening of the stoma, 

 may hit the diflerent parts. 



Ill sections roughly corresponding to line a, the slit of the "Vor- 

 liof" (Fig. 3) is seen to be bounded by two strong, very much 

 cnticnlarized ridges which continue on both sides as a non-cuticu- 

 larized strip united to the cell-wall of the adjacent epidermal-cells. 

 The razor has now passed above the guard-cells without touching 

 them ; the cells seen in Fig. 3 on both sides of the opening, are 

 the subsidiary cells. When sncli preparations are treated with iodine 

 and zinc chloride, the distinction between the cuticnlarised ridge 

 and the non-cuticularised strip into which the latter passes on both 

 sides, becomes perfectly clear. 



Such preparations snggest the comparison of the non-cuticnlarised 

 strip to a ligament of articulation. Preparations of this nature^ treated 

 with iodine zinc chloride show that the guardcells of the stoma, 

 wherever they border on the slit or on the respiratory cavity, are 

 covered with a thin cuticle. 



When a similar preparation, as is seen in Fig. 3, is treated 

 with strong sulphuric acid, conditions such as those shown in 

 Fig. 9 may result. The non-cuticularised "ligaments of articula- 

 tion" are here dissolved ; but the two cnticularised ridges which 

 occur in their normal condition in a and h are still seen, but in c 

 they are separated from one another and have fallen over outward. 

 The thin cuticle which covers the inner side of the guard-cells 

 adjoins these edges. The "ligaments of articulation" are simply the 

 thickened strips of membrane which in Fig. 5 are shown in trans- 

 verse section between the wedge-shaped continuation of the lumen 

 of the guard cell and the subsidiary cell. 



When in preparations [larallel to the surface, the stoma is cut at 

 a lower level corresponding roughly with the line I) of Fig. J, that 

 is to say about in the plane of the "central slit" a view is obtained 

 like that drawn in Fig. 2. The slit is here short and narrow, the 

 inner wall of the guard-cell is clearly thickened where it adjoins 

 the slit. The subsidiaryK'ells at this level surround the guard-cells 

 like a crescent. A section at a lower level, roughly corresponding 

 to line (• of Fig 1, passes under the lumina of the guard-cells with- 

 out touching them. It is then seen, as Fig. (3 represents, that the 

 inner cavity of the stoma is surrounded by two thick ridges of 

 cellulose. The cell-cavities which are seen on either side of these 



