ANATOMY OF ZANTHOXYLUM CLAVA-HERCULIS. "295 



Hypodenii mostly ^-layered, collenehymatic, continuous on both 

 surfaces (rarely interrupted by palisade), replacing the chloren- 

 chyma and forming thick masses above and especially below t lu* 

 mid vein. 



Stereome thin-walled, in narrow plates interrupting the chloren- 

 chyma and extending through the leaf opposite most of the smaller 

 veins; in strong masses above and below the midvein. 



CMorenchyma: Palisade compact, mostly in 2 layers, passing grad- 

 ually into pneumatic tissue of which only the low- 

 est layer is comparatively open and short-celled. 1 



Zanthoxylum clava-herctilis L. 3 



Leaf bifacial, thickish, dark green and shining 

 above. 



Epidermis: Ventral, cells large, walls not undu- 

 late, the outer strongly thickened, the others thin; 

 cuticle sharply defined, delicately wrinkled; sto- 

 matanone; hairs none. Dorsal, cells smaller, the 



. . -, Fig. 43.— Quercus virgini- 



outer walls and cuticle thinner ; stomata with guard a)( „_ s teiiate hair from 

 cells slightly prominent, lying in all directions, dorsal leaf surface. 



-,,, a • n • j • n i- Viewed from above. 



surrounded by 4 to 6 epidermis cells; hairs none, scale 270. 



Hypodermal collenchyma with strongly thick- 

 ened walls in 4 or 5 narrow layers above the midvein; collenchymatic 

 tissue in 4 or 5 wide layers beneath the midvein. 



CMorenchyma: Palisade a single compact layer of short cells; 

 pneumatic tissue in 2 or 3 layers, rather open. 



Oil reservoirs schizolysigenous, 3 scattered through the mesophyll 

 near the ventral surface, and larger ones at the base of each indenta- 

 tion of the leaf margin, surrounded by 2 or 3 layers of thickish-walled 

 parenchyma with cells strongly compressed parallel to the surface of 

 the cavity. 



Mestome bundles surrounded by a thin, interrupted sheath of stere- 

 ome, which is continuous and (in cross section) crescent-shaped out- 

 side the leptome. 



1 Quercus laurifolia Michx. is a deciduous-leaved species, common along the 

 coast and perhaps occurring upon Ocracoke Island. Leaves from Cape Henry, 

 Va., show the following differences from Q. virginiana: 



Epidermis: Cuticle thicker; dorsal surface less densely covered with similar 

 stellate hairs, their arms longer, more slender and much thinner-walled. 



Collenchymatic hypoderm none except above the midvein. True collenchyma 

 t hypodermal) strongly developed beneath the midvein. 



Stereome entirely surrounding the midvein, where it is much thicker- walled 

 than in virginiana. 



CMorenchyma: Only the uppermost layer typical palisade; pneumatic tissue 

 more compact and with more elongated cells than in virginiana. 



-Material from Virginia and Mississippi. 



a Compare Solereder, Syst. Anat., p. 201. 



