1918] THOMPSON—GNETALES AND ANGIOSPERMS 89 
completed, the positions of three bars being indicated by pro- 
jections. In the wood of different species of Vaccinium innumerable 
conditions similar to these may be found side by side. I have been 
careful to determine that none of these cases are due to imperfect 
sectioning, but that they represent the actual state of affairs. This 
has been done by means of careful series of sections in celloidin. 
Moreover, views like e, which are common, could not be produced 
by the carrying away of the bars in sectioning, for in that case the 
margin of the perforation would not be smooth, but would show 
where the bars had been broken. From these facts it is clear that 
the angiospermic vessel with the single large perforation has been 
derived from that with the scalariform perforations. 
Comparison of evolution of Gnetalean with that of 
angiospermic vessels 
We have seen that the single large perforation of the Gnetalean 
vessel has been produced by the fusion of several perforations 
derived from circular bordered pits. We have also seen that the 
similar single large perforation of the angiospermic vessel has been 
evolved from the scalariform type. Evidently, therefore, the two 
are not genetically related. In the evolution of the Gnetalean 
vessel there is and can be no scalariform stage. The Gnetalean 
vessel usually has only two rows of circular pits and never more than 
three. Consequently, no matter how the fusions take place, no 
scalariform bars can result. The Gnetalean and angiospermic 
vessels may or may not have been derived from the same type of 
element, but from the very beginning the evolution of the two has 
taken place along entirely different lines. In the Gnetalean line 
a few circular bordered pits, haphazardly arranged, have enlarged 
and fused in a single perforation; in the angiospermic line long 
narrow parallel slits, which have been retained or evolved, have 
fused to form a similar single perforation. 
Conclusions 
From these considerations it follows that the vessel of Gnetum 
Should disappear from all discussions of the origin of angiosperms. 
The possession of vessels by the two groups can no longer be used 
