Caryophyllacea'. 



261 



the epidermis (it is devoid of stomata and is higher on the 

 dorsal than on the ventral side: A, G, H and /; a few 

 stomata, however, may occur towards the edge of the 

 leaf), and in the sheath round the vascular bundles (yl and 

 D). For the rest, these features may vary somewhat, probably 

 according to the prevailing conditions of the surroundings, 

 but, on the whole, 1 found the structure of the leaves to be 

 similar in plants fromW. and E.Greenland, Iceland and Norway. 



Fig. 16. Silène acaulis. 

 From Iceland: A, B, C, F, G and H. From W. Greenland: D ami E.) 

 A, Transverse section of leaf; lib, bast; d is the dorsal surface, which 

 lias no stomata (see G) and is slightly higher than the ventral surface 

 [v), which has numerous stomata (see //). The forms of the epidermal 

 cells are seen in the same figures. B and C, Transverse sections of leaf. 

 D, Transverse section of vascular bundle; lib, bast. E, Transverse 

 section of leaf, four vascular bundles are seen and three cells with 

 crystals of calcium oxalate. F, Stoma. J, Epidermis of ventral surface; 

 the cell-walls are less undulating than in //. (E. W.) 



That it depends on the direction of the leaves (their 

 position with reference to the light) whether they become 

 isolateral or dorsiventral, was also pointed out by me in 

 1891, in the case of the Honckenya; they are isolateral 

 when directed upwards, and dorsiventral when horizontal. 



