Hybridization of Vitis Rotundifclia 
o 
(Fig. 1), at which there is no diaphragm. The pith is light green in 
color and so dense that Munson (4) in describing it says, “in place 
ot pith a dense, dark green, cellular, nonfibrous wood.” The cells are 
uniform in size in the node and internode, very thick walled and pitted. 
Starch is stored throughout the pith column. 
Xylem. In T . rotundifolia the xylem forms a greater part of the 
stem than any other species (Fig. 3). Moreover, it is distinguished 
from Euvitis species by the character of the wood, which is composed 
oi numerous tracheae or vessels embedded in a mass of wood fibers 
(Fig. 4), both of which are smaller in diameter than those of other 
species, except 1 . munsoniana. These fibers, which are almost round, 
are septate and have extremely thick walls and a very small lumen. 
They are lignified to a greater degree than Euvitis species as is seen 
in the difficulty in cutting the stems, in the staining reaction, and in 
the thick walls. 
The vessels are of considerable diameter (Fig. 4), although the 
smallest to be found in Vitis species, and very long, due to many of 
the cross walls having been dissolved away. The pitting consists of 
elongated horizontal slits closed by thin membranes, as is common among 
vines. These pits are of two sizes depending on whether the vessel is 
in contact with wood fibers or with other vessels. Where the tracheae 
adjoin wood fibers, the pits are fairly small horizontal slits arranged in 
vertical rows. If one vessel is in contact with another, the slits are 
very long, extending almost the width of the vessel. Tyloses occur in 
the vessels, the occluding cells being thin walled, parenchymatous, and 
not pitted. 
Phloem. The arrangement of the elements of the phloem (hard and 
soft bast) in the Muscadinia species differs from that in the Euvitis 
species. Figure 4 is a photomicrograph of a cross-section of a bundle 
showing the phloem and part of the xylem and wood rays. Here in 
V. rotundif olia the phloem as seen in transverse section is triangular 
in outline with the hard bast more or less radially disposed on the sides 
of the soft bast. That is, the portion of the cambium differentiating 
hard bast remains about the same, while the increased circumference 
due to growth is adjusted by an increase in the amount of cambium form¬ 
ing soft bast. This widening of the phloem accompanying the growth 
of the stem results in a triangular-shaped mass of this tissue. The 
hard bast is composed of thick walled septate wood fibers. The cells 
of the soft bast, which are small and thin walled, are somewhat irregu¬ 
larly disposed. 
External to the phloem there is a small round bundle of sclerenchyma 
fibers forming the apex of the triangle mentioned above. These fibers 
are extremely long, nearly round, very thick walled with small lumen, 
and septate. 
