OF THE EASTERN UNITED STATES 379 



walls slightly curvilinear. Over the veins the cells are rectangular 

 and elongated in the direction of the leaf bundles. The mean dimen- 

 sions of these cells are 23.20 nx 15.20 fx. The cuticle is punctated by 

 very small pearls within which, according to Chevalier, (7, p. 113) are 

 associated fine granules of wax. The summit of each epidermal cell 

 forms a rounded projection which together with others give a rough 

 aspect to the surface. The bottom and transverse walls remain thin. 

 The surface of this epidermis contains numerous cr^-pts not any larger 

 than those of the lower epidermis. Some of these crypts contain a 

 stalked golden-yellow balloon-shaped gland, while others possess a 

 stalked reddish-brown bowl-shaped gland which becomes black as the 

 leaf ages. The stalk of the balloon gland is 4-7 cells high and two rows 

 of cells in width. The gland is unicellular and contains oil in its young 

 state which resinifies as the gland becomes older. The stalk of the 

 bowl-shaped gland ordinarily varies from 7-8 cells in height and is 4 

 cells wide on the mature adult leaf. The head or gland is multicellular 

 and contains resin. Very few short unicellular simple trichomes are 

 found. These when present are sclerified at their bases. Scattered 

 here and there on the surface and in the middle of normal cells are isolated 

 refractile elements which represent the bases of these unicellular simple 

 hairs which have broken down on the level with the epidermis and are 

 completely sclerified. Stomata are absent on this epidermis. The 

 mesophyll shows palisade and spongy parenchyma differentiation. 

 The palisade zone is 4-5 cells broad and is composed of columnar elements 

 usually about twice as long as wide. Some of these elements contain 

 rosette crystals of calcium oxalate. The spongy parenchyma region 

 consists of chains of oval to irregular shaped cells surrounding large 

 intercellular air spaces. The fibro-vascular bundle of the mid-rib, as 

 well as smaller vein bundles, run through this region. Each is connected 

 with the upper and lower epidermis by means of hx-podermal cells, many 

 of which are enlarged and contain a rosette of calcium oxalate. The 

 fibro-vascular bundle of the mid-rib is reinforced above and below by 

 an arc of sclerenchyme. The xylem of this bundle is quite broad and shows 

 medullary rays 1-cell wide, which radiate like a fan. The ducts show 

 spiral thickenings. The phloem forms a thick semilunar band below 

 the xylem. 



The lower epidermis consists of polygonal cells whose outer walls 

 are much less cuticularized than those of the upper epidermis. Like 

 those of the upper epidermis they contain a brownish content. Their 

 vertical walls are curvilinear. The mean dimensions of these cells are 



