i9o8.] OF THE SAND DUNE PLANTS OF BERMUDA. 105 



with straight hairs that form an air-still chamber into which the 

 projecting stomata open. The lower epidermis is two- to three- 

 layered, and the whole leaf is decidedly tough and leathery, and thus 

 well adapted to growing on the sand dunes of Bermuda. A dipho- 

 tophyll (Fig. 6, Plate II.). 



Sisyrinchium bennudianuin. — The Bermuda blue-eyed grass is 

 provided with leaves that stand more or less upright, so that the inci- 

 dent rays of light strike the edges of the leaves. The epidermal 

 cells on both the upper and lower morphologic sides of the leaf are 

 thick-walled and the stomata present on both surfaces are depressed 

 the entire width of the epidermal cells. There is no palisade tissue, 

 the loose parenchyma filling the center of the leaf between epidermal 

 surfaces. The vertical leaves are, therefore, isophotic and the leaf is 

 known as a spongophyll. The vertical leaves, the thick epidermal 

 cells and the depressed stomata fit the plant to its environment. A 

 spongophyll (Fig. 7, Plate II.). 



Stenotaphrum americannni. The Bermuda crab grass is a tough, 

 wiry one, well fitted to survive in the driest places on sand dunes and 

 rock faces. The leaf blades arise from sheaths that, together with 

 other overlapping leaf sheaths, form a tuft that arises from the nodal 

 regions of the wiry, prostrate, creeping stem. The blades are more 

 or less erect and folded partially lengthwise, with the upper side 

 innermost. The spike of closely set flowers is slightly bent, sug- 

 gesting a crab's claw. The upper epidermis consists of large, open 

 papillate cells. The loose parenchyma fills the leaf section and the 

 under surface of the leaf has a thick epidermis with numerous 

 stomata, provided with small guard cells reenforced by two secon- 

 dary cells. The bundles are toward the upper side. The vertical 

 isophotic leaf consequently becomes a spongophyll. The adapta- 

 tions to the environment are upright, rolled leaves, thick lower epi- 

 dermis and overlapping, tufted leaf sheaths (Fig. 8, Plate II.). 



Heliotropium curassavicum resembles in its unilateral cymose 

 inflorescence the common heliotrope. It is a slightly woody plant 

 that grows about a foot or two tall, with alternate, narrow, oblanceo- 

 late leaves. The cells of both the lower and upper epidermis are 

 thin-walled, with slightly sunken stomata on both sides. The chlor- 

 ophyll bearing cells of the leaf (the chlorenchyma) are arranged so 



