1899] MICROSCOPICAL JOURNAL 35 



section is 14 2-3 mm. and the average width is 10 mm. their 

 average length is 252 1-5 mm. In cross section the "thin- 

 walled" cells above referred to are 16 2-3 mm. long and 8 

 mm. wide. The strengthening cells vary greatly both in 

 size and shape. The average length in cross section is 

 18 2-3 mm. and the average width is 15 1-3 mm. A no- 

 ticable difference between the epidermal cells and the 

 other cells of the region is in their length. The strength- 

 ening and thin-walled cells are much shorter than the ep- 

 idermal cells. The average length of the strengthening 

 cells is 108 mm. 



The Stomata. — These are arranged in rows along the 

 surface of the leaf. The dorsal side of the leaf has more 

 stomata than the ventral side. In a space of 1332 square 

 mm. on the ventral side of the leaf there is an average of 

 164 stomata. In a space of similar size on the dorsal 

 side there are 172 stomata. Tli6 guard-cells are depress- 

 ed below the surface of the leaf and are almost on the 

 same plane as the innermost row of strengthening cells. 

 A thin surface section of the epidermis shows merely the 

 mouth of the stoma looking like a small round opening in 

 the epidermis. To obtain a view of the guard-cells in the 

 tangential section, a thin section of the epidermis must be 

 first removed. The s'toma in tangential section is illipti- 

 cal in shape, fig. n, 1. Measured through the centre it 

 averages 46 2-3 mm. in width and 58 2-3 mm. in length. 

 The guard-cells, as seen in transverse section, are almost 

 oval in shape, with the exception of a slight extension on 

 the end lying towards the mouth of the stoma, fig. M. 

 These cells have very thick walls. A sharp prolongation 

 extends from each guard-cell slightly above the epider- 

 mis, thus forming a small cavity between the surface of 

 the leaf and the guard-cells. Below the guard-cells is 

 the respiratory cavity, which has an average depth of 

 45 2-3 mm., fig. m, 2. 



Mesophyll. — The greater part of the leaf is composed 



