igi2] STARR— ANATOMY OF DUNE PLANTS 297 



Table (I) on p. 298 gives a comparison of mesophytic and dune 

 forms of the same species with respect to eleven characters of 

 the leaf. 



A summary of leaf characters is as follows: 



Hairs more abundant 12 X (3 same) 



Surface of upper epidermal cells greater 9 X- 5 M (2 same) 



Depth of upper epidermal cells greater 5 X-i 2 M (4 same) 



Side walls of upper epidermal cells wavy 6 X-i 1 M 



Side walls of lower epidermal cells wavy 8 X-16 M 



Outer wall of epidermis heavier 18 X (2 same) 



Cuticle ridged 10 X- 6 M 



Palisade more completely organized 17 X (1 same) 



Better development of conductive elements 15 X- 2 M (1 same) 



Heavier sclerenchyma 14 X- 1 M (1 same) 



Heavier collenchyma 17 X 



tion of those of Populus balsamifera, 

 than in the mesophytic. The poplar 

 growing alone at the side of a road, so the exposure was greater 



form 



collected. 



most of the meso 

 , also were thicker 



the 



The greater extent of surface in the upper epidermal cells in the 

 majority of the dune forms is striking. Grevillius speaks of 

 epidermal cells in the alvar plants being smaller than in the normal, 

 but he may have used the lower surface only, as he mentions the 

 subject in connection with stomata, and that may differ from the 

 upper surface. Cuticular transpiration is reported as taking place 

 from the side walls of the epidermal cells more abundantly than from 

 the lumen of the cell. If this is true, then increase in the surface 

 extent of the cell would decrease cuticular transpiration. The 

 apparent thickness of the epidermis of dune forms is due to the 

 heavy wall and cuticle and not to the depth of the cells. Waviness 

 of the side walls seems to be related to shade, as it occurs more 

 frequently in mesophytic leaves, and in mesophytic leaves on the 



under 



thickness 



Deep, compact palisade, well developed conductive elements, 



ma 



