HISTOLOGY OF HYPERICUM PTLOSITM. 495 



ASCYKUM STANS Michx. 



Cleared land (non cultural), Herbaceous formation, preferring rather 



moist soil. 



Leaf nearly erect (when growing where it is exposed to strong light), 

 bifacial. 



Epidermis: Ventral, cells large, with rather thick walls, the radial 

 ones not undulate. Dorsal, radial walls slightly undulate; cuticle 

 bearing a coating of wax. Stomal a on the dorsal surface only, lying 

 in all directions, sunken, each bordered by three to five ordinary epi- 

 dermis cells, 1 the guard cells with thick cuticle. Hairs none. 



Palisade in one layer; then two layers of tissue, similar but not 

 compact; then open pneumatic tissue with low cells. Secretion cav- 

 ities in the mesophyll near the ventral surface. 



Hypoilermal eollenclujmatie tissue well developed above, and espe- 

 cially below the midvein. 



Hypericum virgatum Lam. 



Cleared land (non cultural), Herbaceous formation, often with the 

 preceding. 



Leaf small, erect, and often somewhat appressed to the stem, 

 isolate ral. 



Epidermis much alike on both surfaces, the cells comparatively 

 veiy large, their radial walls slightly undulate on the ventral surface, 

 more so on the dorsal; cuticle granular. Stomata on both faces, more 

 numerous on the dorsal, mostly parallel to the veins, sunken, each 

 bordered by three (rarely four) undifferentiated epidermis cells. 

 Hairs none. 



Palisade in one layer on each side of the leaf, 2 inclosing the thin, 

 central stratum of nearly colorless pneumatic tissue. Large secretion 

 cavities present in the mesophyll. 



Hypodermal coUencliymatie tissue above and below the midvein. 



Stereome none. 



Hypericum pilosum Walt. 



Cleared land (noncultural), Herbaceous formation, growing in dry, 

 sandy fields. 



■ Leaf much like that of IT. virgatum as to position, but densely 

 pubescent, isolateral (fig. 87). 



'Compare Vesque (Comptes Rendus, vol. 100, p. 1080), who says, "The Hyperi- 

 cums are characterized by stomata bordered by three epidermis cells." 



^H. virgatum and II. piloxiim (see below) are exceptional among Hypericaceae 

 in the isolateral structure of their leaves. Solereder (Syst. Anat., p. 184) describes 

 the mesophyll in this family as. "so far as is known, bifacially arranged." He 

 further says (p. l-l!)) that "stomata in the Hypericaceae are present only on the 

 underside of the leaf." 



