1912] STARR— ANATOMY OF DUNE PLANTS 271 



Opuntia Rafinesqui. — Stem 



outer 



wall of epidermis 8/* thick, cuticle 2.4/*; several hypodermal 

 layers of small heavy- walled cells; the chlorenchyma composed 



many 



stem 



difficult 



dry it out even with heat and pressure; vascular system poorly 

 developed; walls of the elements thin. 



Shrubs 



pumila 



directions 



and thus important in helping to make dunes stationary. Leaf 

 thick, 216 /*-; outer wall of epidermis 5-6 /*; cuticle very thick, 

 ridged on the lower surface, the ridges so high that they fray out 

 along the edge; cells above and below the midrib papillate and 

 cuticle smooth, 8 //. ; heavy masses of collenchyma above the stele of 

 the midrib and several layers below, also in other large veins; great 



elements 



the 



lower cells of mesophyll 



palisade-like; crystals, oil, and other deposits abundant. Stem 



numerous 



small lumen; groups of sclerenchyma in the cortex; cork thick. 

 Salix syrticola.~A shrub with the same habits as Prunus pumila 



with 



ermis 



ma 



epidermis on both sides; two layers of palisade next the 



epidermis and three more 



Stem 



with medullary rays very narrow; vessels not large but numerous; 

 fibers heavy, with small lumen; outer layer of pith sclerenchyma- 

 tous; outer layers of cortex collenchyma tous; three rows of mechani- 



m 



Hudsonia tomentosa.—A bushy, heathlike shrub. Leaf small, 



the 



upper epidermis composed of large cells; palisade about one-half 

 the mesophyll of the narrow part of the leaf. Stem hairy, very 

 woody, the vascular cylinder occupying most of the diameter, com- 

 posed of very heavy fibers and few vessels; a few large scleren- 



