Relationships of the Gnetales . 1087 
standpoint of evolution with any special members of that family. It would 
seem rather to be related to some generalized ancient form. 
2. Vessels. 
The fact that Ephedra possesses true vessels is perhaps its best known 
anatomical feature. It is also well known that the perforations of those 
vessels correspond to the bordered pits of tracheides. The further fact that 
there are interesting transitions between bordered pits and perforations has 
been emphasized by Strasburger 1 and by Boodle and Worsdell. 2 The 
writer’s study has shown that the transitions between tracheides and vessels 
are much more complete than was suspected, and has revealed additional 
structural features. For the sake of completeness some facts already known 
will be briefly recapitulated. 
The lumina of the vessels vary from that of a tracheide to many times 
that size (PI. XCVI, Figs. 27 and 29). The pits on the lateral walls are 
identical with those of the tracheides, though arranged more often in two rows. 
In addition the vessels show the bars of Sanio , tertiary spirals, and trabeculae 
characteristic of the tracheides. The perforations of the end walls are seen in 
transverse section (PI. XCIV, Fig. 10) to be simply enlarged bordered pits 
in which the border has become narrow and the torus has disappeared. In the 
radial section (Fig. 12 and PI. XCVI, Fig. 25) these points are also visible, 
although the border is not so clear. The perforations may be in two or three 
rows which are opposite or alternate. Perhaps the clearest ideas may be 
obtained from the tangential section which has been photographed in 
PI. XCV, Fig. 17. In this figure the slanting end wall, the open com- 
munication between the conterminous elements, and the border of the 
perforations are clearly shown. 
From the appearances presented in these figures the conclusion is 
natural that the perforations represent modified bordered pits. This 
assumption is rendered a certainty by the fact that one frequently finds true 
bordered pits in series with the perforations (see Fig. 20). The latter in such 
cases occupy the position of the bordered pits of a normal tracheide. This 
condition is shown in tangential view in Fig. 18, in which the two bordered 
pits at the bottom of the end wall have well developed borders and tori. 
The transitions between tracheides and vessels are in fact remarkably 
complete, especially in the first few annual rings. In Fig. 19 is represented 
an element which differs from a tracheide only in the absence of the torus 
and narrowness of the border of one of its enlarged central pits. The other 
pits, while showing a slight decrease in the border, are still true bordered pits. 
A further stage is represented in Fig. 20, and many other figures could have 
been presented showing all stages up to the completed vessel of PI. XCVI, 
1 Uber den Bau und die Verrichtungen, &c. 
% loc, cit. 
