82 HARSHBERGER— LEAF STRUCTURE OF [April 23. 



and 12c) are not sunken below the general surface. The upper 

 epidermal cells are large, irregular in size and rounded. The lower 

 epidermal cells are irregular and consist of bulliform with spiny 

 hair cells opposite the leaf veins. The leaf exhibits a typic spongo- 

 phyll structure. 



Xanthium echinatum (Plate IV, Figs. 13 and 13a). — The cockle 

 bur has broadly ovate, cordate leaves and the whole plant is rugose, 

 especially the leaf surfaces. The upper and lower epidermal cells 

 are thin-walled and provided with stout, projecting, multicellular 

 hairs. The palisade cells extend through the leaf except a narrow 

 row of cells near the center. Although this leaf has been classified 

 as a diplophyll, yet it might with equal propriety be called a 

 staurophyll. 



Quercus obtusiloba (Plate IV, Fig. 14). — The post oak is a com- 

 mon tree in the pure dune sand of the New Jersey coast. The 

 leaves are obovate in outline, 1-2 dm. long, the usually fine lobes 

 spreading, the middle pair of sinuses are deep, wide and obliquely 

 rounded at the bottom of the lobes. The leaves are leathery, thick 

 and shining with scattered hairs above, densely gray, or yellowish 

 hairy beneath. The epidermal cells are small with thick cuticle 

 and the lower surface shows the presence of multicellular hairs. 

 The palisade rows numiber from two to three and the loose paren- 

 chyma is compact. The leaf is a typic diphotophyll. 



Quercus falcata (Plate IV, Figs. 15 and 15a). — The Spanish 

 oak has leaves which are prolonged into a more or less scythe- 

 shaped lobe with the under leaf surfaces grayish-downy or fulvous. 

 The upper epidermal cells are large and thin-walled, as are also 

 the lower epidermal cells. From the lower surface, a lot of com- 

 pound hairs project, the tines of which are straight, sharp-pointed 

 cells. The stomata are not depressed and a single row of palisade 

 cells is present, so that the leaf is a typic diphotophyll. 



Vitis Labrusca (Plate IV, Figs. 16 and 16a). — The northern fox 

 grape has large leaves which are entire, or deeply lobed, slightly 

 dentate. They are rusty-wooly beneath. The vines begin their 

 growth on the forest trees, and as the sand drifts in around them, 

 the grape vine branches grow out in a prostrate manner over the 



