1921] BLISS—VESSEL IN SEED PLANTS 321 
In the Vitaceae the lateral walls of the vessels i in contact with 
other vessels are practically ll This condition 
is of particular interest because the sihlathouns lateral sculpture of 
vessels is a phenomenon of rare occurrence in most angiospermous 
orders, being usually confined to a single genus and occasionally to 
a single species. If we examine the primitive region of the stem 
near the primary wood, vessels with pitted lateral walls may often 
be found (fig. 37). A further fact which has some bearing on the 
situation is the occurrence of pits on those walls of the vessels 
which are in contact with the vasicentric parenchyma, character- 
istic of this group. This situation is not the less striking because 
ray cells and even longitudinal parenchymatous elements in the 
Angiosperms in general are frequently related to vessels by means 
of fusion pits of a scalariform nature. This condition is wide- 
spread among the Angiosperms. It has been pointed out by BaILey . 
(x) in this connection that in modern species of Pinus the lateral 
pits of the rays often undergo fusions. Similar conditions are often 
found in the Podocarpineae, Taxodineae, and Cupressineae, and 
has even been found in Paleozoic Gymnosperms. Fig. 38, illustrat- 
ing the same section as fig. 37, farther out from the primary wood, 
shows the type of vessel characteristic of the mature wood of the 
Vitaceae as a group, with scalariform sculpture. It is apparently 
quite clear that the vessel with scalariform lateral pits in the 
Vitaceae has been derived from a pitted predecessor, and that it 
is not a primitive vessel type in this family. 
Turning now to the perforation of the vessels in the Vitaceae 
in the mature wood of Leea and Vitis, the vessels are characterized 
by large open terminal pores. This confirms SOLEREDER’S state- 
ment that the vessels in the Vitaceae ‘‘have simple circular or 
elliptical perforations.” Such a perforation is seen in the radial 
section of the stem of a species of Leea in the region of the primary 
wood (fig. 36) at the right of the figure. A very interesting fusion 
scalariform perforation is seen in the vessel on the left. The 
photograph in this case is not clear, owing to the thickness of the 
section, but seen under the microscope it is an unusually vivid 
demonstration of the course of events in the evolution of the open 
