Caryophyllaceæ. 



265 



Moreover, the mesophyll which hes under the epidermis 

 differed on the two surfaces {E and G). In a specimen from 

 S. E. Greenland there was almost homogeneous, but indis- 

 tinct, palisade-tissue on both sides. 



Similar weak dorsiventrality I found also in Cerastium 

 trigynum (Fig. 20), and Minuartia biflora, which latter may 

 however have decided isolaterality (Fig. 21, К and B), but 



Fig. 20. Cerastium trigynum. 

 (From Iceland; С H. Ostenfeld.) 

 A, Transverse section of leaf; pa, palisade-tissue. B, The transverse 

 section shows the very lacunose structure of the thin-walled mesophyll ; 

 the epidermis of the dorsal surface {d) is higher than that of the ventral 

 surface; there is a distinct sheath around the vascular bundle; there 

 are about two layers of palisade-cells; g, a cell with crystal of calcium 

 oxalate. C, Transverse section of stem. The black ring indicates the 

 place of the mechanical tissue. There are five lacunæ in the cortex. 

 D, From ventral side; epidermis and palisade-cells. E, From dorsal 

 side. Magnification of D and E is the same, so that it is distinctly 

 seen that the epidermis of the dorsal surface is thicker than that of 

 the ventral surface. F, The epidermis of the ventral surface and trans- 

 verse section of palisade-cells. G, The epidermis of the dorsal surface. 



(E. W.) 



it differs in the epidermis of the two surfaces, which, as it 

 however appears, cannot be connected with the fact that 

 the leaves may be directed upwards, with the ventral surface 



