8 
Hybridization of Yitis Rotundifolia 
usually somewhat brittle. It is not as hard as V. rotundifolia hut 
seldom as soft as V. vinifera. The specific gravity in all but two 
cases was greater than 1.0, and hence fresh-cut wood sinks in water. 
In cross section the stem is more or less elliptical rather than oblong 
as the V. vinifera parent, hut not often as round as in V. rotundifolia. 
Pith. The diameter of the pith column of the hybrids is a little less 
than the average of the two parents and it varies in color from light 
green to light brown. The size of the pith cells at the internode is 
about the same as in V. rotundifolia, hut those at the node vary in 
size with the extent to which there is an expression of a diaphragm. 
In a small percentage of the hybrids (two of the twenty-six examined) 
there was a distinct diaphragm at the node visible to the naked eye. 
In the others there was a tendency for the cells at the node to be com¬ 
pacted in a vertical direction. In order to arrive at some conclusion as 
to the extent of this compaction the number of cells in a given area in 
an average region of the longitudinal section was counted. The results 
are given below: 
TABLE 3 
Vine 
Number of Cells at 
Ratio 
Node 
Internode 
Vinifera 
227 
89 
2.54: 1 
Rotundifolia 
135 
136 
1.00: 1 
Hybrid with diaphragm _ 
138 
40 
3.45: 1 
Hybrid without diaphragm 
139 
88 
1.58: 1 
The above table would indicate that the cells of the internode resemble 
the T. rotundifolia parent, and that the cells at the node are more or 
less influenced by the V. vinifera parent. It was also observed that 
the increase in the number of cells at the node was due to a lessening 
of their vertical height with little change in their horizontal diameter. 
Xylem. The character of the xylem is intermediate between that 
of the parents. The hybrids vary, however, through all the range, one 
in fact going beyond V. vinifera in size of cells and number of vessels. 
The fibers are larger than in V. rotundifolia but not as angular as in 
r. vinifera. The tracheae also are larger than those of V. rotundifolia 
and the sculpturing is that typical of Yitis species. Some of the 
variation in the size and number of vessels of the hybrids is shown in 
Figures 7-10, and 13-38. 
Phloem. In hybrids the arrangement of the elements of the phloem 
as seen in the transverse section covers the ranges of both parents. 
There is, however, a greater resemblance to the staminate parent in the 
majority of cases. In most of the vines there is a radial row of hard 
hast of greater or less extent on the sides of the phloem bundle (Figs. 
7 and 8). In addition to this, there is also a tendency for tangential 
