6 
Hybridization of Vms Rotundifolia 
Rays. The rays of all Vitis species are of the compound wood ray 
type common in vines. These are several cells wide and extend longi¬ 
tudinally through the internode and are full of starch (Fig. 4). Those 
of V. rotundifolia are not as broad as the ones of the Euvitis group. 
The most significant characteristic as contrasting with the other Vitis 
species is that portion of the ray extending between the phloem bundles. 
In V. rotundifolia the ray in this region expands by cell multiplication 
to fill the widening gap between the phloem as the stem increases in 
circumference (Fig. 4). This is clearly evident in the arrangement of 
the cells which here are formed in tangential rows, contrasting with 
the radial rows of the ray proper. 
Cortex. The cortex in V. rotundifolia is in sharp contrast with that 
of the bunch grape type (Fig. 4), and the seat of this difference lies 
in the phellogen or cork cambium. In the Muscadinia species the 
pliellogen is formed immediately under the epidermis, and produces 
internally the phelloderm of varying thickness. This is composed of 
parenchymatous cells in irregular longitudinal rows. V. rotundifolia 
is further characterized by the presence of numerous lenticels which 
penetrate the cortex for a considerable depth opposite the ends of the 
rays (Fig. 4). 
VITIS VINIFERA 
Bark. The bark of V. vinifera is red-brown to greyish-brown in 
color on the young wood. It is finely striated and sheds in long fibrous 
plates. 
Wood. The wood is very soft and porous. It is light in weight 
(specific gravity less than 1.0), quite brittle, and more or less oblong 
in cross section. 
Pith. The diameter of the pith column in comparison with that of 
the stem is much greater than in the case of V. rotundifolia. Figure 
5 of V. vinifera, which is of the same magnification as Figure 3 of 
V. rotundifolia, shows the proportion of the tissues in section. The 
pith cells of V. vinifera, as may be seen in a comparison of these two 
photomicrographs, are much larger and thinner walled. The pith is 
dry and light brown in color and contains little or no starch. At the 
node, there is a distinct diaphragm (Fig. 2) composed of thick walled 
lignified cells with pitted walls. 
Xylem. The elements of the xylem (vessels and wood fibers) are 
larger in diameter than are those of V. rotundifolia. This is best seen 
by contrasting Figure 5 with Figure 3. The wood fibers are more 
angular in section and not as thick walled, nor as lignified, and are 
in more distinct radial rows (Fig. 6). There are more vessels and 
they are larger in this species than in V. rotundifolia, but the sculptur¬ 
ing is similar. Tyloses in the vessels are common in this species. One 
occluded vessel may be seen in cross section at the lower right in Figure 
6 and several in Figure 5. 
