34 THE AMERICAN MONTHLY [Feb 



embedded in paraflBne hy the usual methods, and sections 

 were cut with the microtome. The sections were double 

 stained with eosine and gentian-violet. In examining a 

 transverse section from the periphery towards the centre, 

 three distinct regions can be easily identified. These 

 regions are the cortical, fig. b, 1, the mesophyll, fig. b, 2, 

 and the fibro-vascular, fig. b, 3. The average long di- 

 ameter of a transverse section is 1.6 mm., and the aver- 

 age short diameter is 0.8 mm. 



Cortical Region. — The cortical region includes epi- 

 dermal and hypodermal or "strengthening cells" and the 

 guard cells of the stomata. Along the angles of the leaf 

 are serrations perceptible to the touch, fig. g. These ser- 

 rations are prolongations of the epidermal cells with the 

 cuticle greatly thickened. 



The number of rows of cells in the cortical region va- 

 ries. The dorsal side of the leaf has from three to four 

 rows of cells, fig. E, while the ventral side has from two 

 to three rows, fig. r. There is only one row of epider- 

 mal cells proper, fig. c, 1. In some places one, and in 

 others two rows of strengthening cells are found. The 

 row of cells immediately underlying the epidermal cells 

 is somewhat difl'erent in appearance from the other cells 

 of the region, fig. c, 2. In transverse section, they ap- 

 pear somewhat elliptical in outline, and are filled with 

 granular contents. The epidermal cells have a greater 

 uniformity of shape than the other cells of the region. 

 The outer wall of these cells is curved bow-fashion and 

 the inner wall is curved or straight according to the char- 

 acter of the wall of the adjoining cells. In tangential 

 section the cell walls of the cortical region, perpendicu- 

 lar to the surface of the leaf, are sinuous, but the walls 

 parallel to the surface are straight. Accordingly in radial 

 longitudinal section and also in transverse section the 

 cell walls are plane, but in tangential section they are sin- 

 uous. The average length of the epidermal cells in cross 



