440 BOTANICAL GAZETTE [JUNE 
About this perforation is a well defined border, and except for a 
vestige of a cross wall that runs into it from the left, we should 
find here the simple large open perforation which is the result of 
complete fusion; in other words, the type characteristic of the 
more advanced species of Gnetum. ‘The vessel below shows an 
imperfect perforation resulting from the more or less complete 
fusion of a number of large open bordered pits. 
Fig. 3 presents a higher magnification of two large vessels, 
the one to the extreme left showing a group of four large tracheary 
pits arranged suggestively for fusion. To the right is a vessel with 
a single large opening as its perforation, this being the typical 
condition in more advanced species of Gnetum. The border is 
distinct, and by its slightly irregular outline, which shows especially 
well at the upper right side of the perforation, reveals its origin 
from a type like the vessel on the left in the same figure. Fig. 4 
is a high magnification of an intermediate stage of fusion, showing 
the remains of a transverse process about to disappear. 
Angiosperms 
In Angiosperms the evolution of the vessel from the tracheid 
proceeds along the same lines as in Gnetales. Fig. 5 shows the 
organization of the mature wood in Alnus japonica. Here is seen 
the scalariform perforation characteristic of the Betulaceae and 
other presumably primitive Angiosperms. The pits, which are 
many and crowded, have fused in horizontal rows to form scalari- 
form pits. The condition is seen even more clearly to be decidedly 
scalariform under higher magnification, as in fig. 6. 
A section through the medullary region of Alnus japonica is 
shown in fig. 7. This is a rather low magnification, but shows 
clearly the primitive spiral and scalariform tracheids to the left. 
The three vessels to the right of these tracheids show all transitional 
stages from small pits to the scalariform perforations. The 
occurrence of this form of vessel perforation side by side with sca- 
lariform tracheids proves that it is indeed a primitive type for this 
genus of the woody Angiosperms. Fig. 8 shows these same vessels 
and tracheids under higher magnification. Fig. 9 is still another 
