STUDIES OF THE DEVELOPMENT OF PEPEROMIA HISPIDULA 325 
blade thus approaches the peltate type. Over the upper surface of 
the lamina, chiefly near the edges, are scattered some 10 to 25 bristle- 
like hairs of 10 to 20 cells each, and of about one millimeter in length 
(figs. 1,3). The whole leaf has almost the aspect of that of a large 
hydrophytic bryophyte. As the hairs mentioned are not easily wetted 
it seems possible that these and the hairs at the base of the petiole may 
serve to prevent the adherence of water to the surface of this denizen of 
very damp habitats. It is also possible that these hairs may serve 
as an obstruction to small insects creeping over the plant. 
The internal structure of the vegetative organs is also relatively 
very simple. The delicate, sparsely branched roots have a small, 
thin root-cap (fig. 4). The youngest root hairs are found about two 
or three diameters of the root behind the apex of the latter. These 
hairs may reach a diameter of 10 or 12 fi and a length of a millimeter 
or more (fig. 6). Fungus hyphae enter the root from without and 
push among and into the cortical cells. These hyphae are little 
branched, thick-walled, non-septate and from 4 to 5 /z in thickness. 
Coiled tangles of these fungus threads with beadlike swellings are 
found in the layer of the cortex just outside the endodermis (figs. 5, 6, 
7}. In some places the hyphae become greatly swollen to form sac-like 
expansions that may become 15 m in diameter and 54 fx long (fig. 8). 
Whether these hyphae have the function, as well as the appearance, of 
an endophytic mycorhiza cannot yet be stated with certainty. 
The oldest roots seen still had some root hairs on them ; the epider- 
mis was intact and the outer walls of its cells were but slightly thickened 
or cutinized. The cells of the epidermis are 20 or 25 fjL in radial and 
tangential thickness and 50 or 60 fi long (figs. 5, 6). The cortex of 
the mature root is of 5 or 6 layers of cells, which are 12 to 40 )U in diam- 
eter and ICQ to 150 /x long. There are numerous intercellular spaces 
between the cells of the inner layers of the cortex. Many of these 
are occupied by the fungous hyphae mentioned above (fig. 6). The 
radial walls of the endodermis are but slightly thickened but are 
markedly crinkled, as may be seen in a tangential section (figs. 5, 9). 
These cells are 12 to 20 /x in diameter and 150 ,u long. 
The whole central cylinder of the mature root is only 90 or 100 /x 
in diameter and consists of but 40 or 50 cells in cross section (fig. 6). 
Of these cells two or three are differentiated as water-conducting 
elements. One, at the center of the stele, is a vessel 12 or 15 in 
diameter and with ring-like and spiral thickenings on its walls. A 
