134 AMERICAN MIDLAND NATURALIST. 
the epidermis persists and is very thickwalled. There is no cork, 
and the cortex is collenchymatic throughout, the pericycle is very 
strongly developed with heavy layers of stereome and sclereids, 
while the stele is narrow, surrounding a thickwalled, starch-bear- 
ing pith. 
The mechanical tissues, collenchyma and stereome, are thus 
well represented in the stem of Myssa, the former pertaining to 
cortex, the latter to the pericycle, or inside the hadrome as libriform. 
It is, also, of some interest to notice the superficial cork, and the 
occurrence of calcium oxalate as single or aggregated crystals in the 
cortical parenchyma. 
THE LEAVES. 
When cotyledons are aerial and foliaceous* they generally 
assume the same, or approximately the same structure as the leaves 
proper. They are mostly glabrous, however, and the chlorenchyma, 
sometimes, shows a less pronounced differentiation as palisade and 
pneumatic tissue, beside that the veins are frequently embedded and 
not projecting on the dorsal face. In speaking of Nyssa sylvatica 
the cotyledons doin some respects, possess a structure, which is 
rather distinct from that of the mature leaf of the tree, but not so 
much from that of the primary leaves, which I have drawn in figure. 
1 (L'-£?). 
The principal distinction consists in the structure of the epider- 
mis which, on both faces of the blade, exhibits undulate lateral cell- 
walls (Fig. 10), while in the leaves of the tree, these walls are 
nearly straight (Fig. 12) ; another distinction consists in the much 
larger size of both stomata and epidermal cells in the cotyledons, 
when compared with the mature leaves; this may be readily seen 
from the figures (Figs. ro and 12) which are drawn to the same 
magnification. Thereare no hairs, and the leaf-structure is bifacial 
with a ventral palisade tissue, and a dorsal pneumatic. The midrib 
contains a single collateral mestome-strand surrounded by a thin- 
walled, barely stereomatic pericycle and a parenchyma of thinwalled 
cells destitute of chlorophyll; the secondary and tertiary veins 
are completely embedded in the chlorenchyma and provid- 
ed with typical parenchyma-sheaths; no idioblasts and no 
es 
* Merck's Report Dec, 1909. 
