86 BOTANICAL GAZETTE [JANUARY 
the pits have fused on the side of one element but not on the side of 
the other. In fig. 8¢ all have fused in a common perforation on one 
side but only in groups on the other. In fig. 8d the process is nearly 
completed, the indications of the individual perforations being 
visible only along the left side. In different vessels all sorts of con- 
ditions with respect to the fusion of perforations may be observed. 
In some cases they first fuse horizontally and in some cases 
vertically. 
Fic. 8.—Series of vessels from node of seedling of Gnetwm moluccense, illustrating 
ote ici between Ephedra type and Gnetum type of vessel. 
Evolution of the angiospermic vessel 
li there is any genetic relationship between the Gnetalean and 
angiospermic vessels, we should find in the primitive types of the 
latter a course of development similar to that just outlined, or at 
least some vestiges of the Gnetalean condition: 
The primitive type of angiospermic vessel is undoubtedly the 
so-called scalariform kind (illustrated in fig. 9 from the wood of 
Betula lutea). The most advanced type is the familiar porous kind 
with a single large perforation (fig. 10). In the scalariform type 
the perforation of the end wall is crossed by a large number of 
parallel horizontal bars, or, in other words, there are many hori- 
zontally elongated perforations. The outline of the whole per- 
forated area is similar in shape and size to the single perforation of | 
