HISTOLOGY OF ACER RU1JRUM. 493 



ing the leptome of the larger mestome bundles, in two or three small 

 groups adjoining the hadrome. 



Tlex lucid a (Ait.) Ton-. & Gr. 



Hygrophile Forest formation. 



Leaf thick, persistent, bifacial. The material examined was in an 

 advanced stage of development. 



Epidermis: Ventral, cells small, radial walls thick and porous, 

 straight; cuticle massive, especially above and below the midvein, 

 then' about equaling, with the cellulose layer of the wall, the height of 

 the lumina of the epidermis cells. Dorsal, cells as on ventral surface; 

 cuticle thinner, except beneath the midvein, where it considerably 

 exceeds the lumina of the epidermis cells in height. Stomata con- 

 fined to the dorsal face, apparently less numerous than in I. glabra, 

 lying in all directions, the whole stoma considerably larger than each 

 of the five to seven bordering epidermis cells. Hairs, as in I. glabra, 

 only on the ventral surface along the impressed larger veins (espe- 

 cially the midvein) having a massive, roughened cuticle and an 

 almost obliterated lumen. 



Palisade much as in ./. glabra, three-layered, occupying about one- 

 half the leaf's thickness, very compact, the cells about twice as high 

 as they are wide. Pneumatic tissue less open, with smaller lacunes 

 than in T. glabra. 



Hypoderm (as iu Lopaca) in a single layer above the- midvein. 1 



Beneath Ihc hypoderm occur about two layers of ehlorenehyma 

 with nearly isodiametric cells. On the dorsal surface beneath the 

 midvein there are five or six layers of thick-walled collenchyma. 



Stereome very thick- walled, in interrupted bands above and below 

 the midvein, which is composed of several radially arranged mesfome 

 bundles; but only on the leptome side of the small veins, each of 

 which consist of a single bundle. 



Leaf margins containing neither stereome nor collenchyma, but 

 strengthened by the great thickening of the cuticle. 



Acer rubrum L., var. 



Hygrophile Forest formal ion. 



Leaf bifacial, dark green and somewhat shining above, white- 

 glaucous beneath. 



Epidermis: Ventral, cells with nonundulate radial walls. Dorsal, 

 cells much smaller; cuticle covered with wax. Stomata confined to 

 the dorsal surface, lying in all directions, very numerous, level with 



'Not, as in I. aquifolium, occuring under the epidermis of the entire ventral 

 surface. In that species the hypoderm is described by Lalanne (Feuilles persist - 

 antes. p. 5">) as a second layer of epidermis. But Pfitzer (Pringsheim's Jahrb.. 

 vol. 8, p. 51 ) . who studied its development, found it to be true hypoderm. originat 

 ing from tissue beneath the epidermis. Its cell walls are moderately thickened 

 collenchymatically. 



