1079 
Relationships of the Gnetales . 
Ephedra and the Equisetales can have no evolutionary connexion, but they 
furnish an interesting case of parallel development in plants of similar 
habit. 
Primary Vascular Bundles and Leaf-Traces. 
The bundles of the primary wood, though not large, are rather 
conspicuous in transverse sections. Fig. i gives their appearance in 
E. monostachya. They may be seen to consist of two pairs of large bundles 
and two groups of three smaller ones. The groups of large and small 
bundles alternate regularly. The number and arrangement are constant for 
each species, but vary in the different species. The reasons for the appear- 
ance which they present in transverse sections are readily understood when 
one follows their course by means of a series of sections. 
i. Course. 
The simplest condition is found in E. distachya , and is represented 
diagrammatically in Text-fig. i, which is a reconstruction drawn after 
a study of complete series of celloidin sections through the node. 1 As we 
shall see, it differs considerably from the conceptions arrived at by former 
investigators, but owing to the exactness of the method and the number of 
repetitions the writer feels certain of its accuracy. The ring of bundles is 
represented as split and turned into one plane. In the internode there 
are two pairs of large bundles as in E. monostachya , , but the smaller bundles 
are also in pairs instead of groups of three. There are therefore two pairs 
of large bundles alternating with two pairs of small ones. As the node is 
approached, the smaller bundles flatten tangentially, and short tracheides 
appear between them. By this means they are soon united, so that 
a continuous band of primary wood results. The appearance of this band 
in another species is shown in Phot. 4. The original bundles are near the 
end of the band. Very soon the adjacent large bundle on each side 
becomes included in the same way. Meantime a similar band has been 
formed on the opposite side of the stem. Finally, these two bands become 
united by the extension of their ends. There results a complete girdle of 
nodal wood broken only by the exit of the leaf-traces. Often the position 
of the internodal bundle is indicated by a slight thickening of the girdle. 
The leaf-traces, of which there are two at every node to supply the pair 
of opposite leaves, are in all cases double. The double character is shown 
in transverse section in Figs. 5 and 6, and in tangential section in Fig. 7. 
In the latter figure the two strands of the trace are below the centre of the 
field which is occupied by the large branch gap. The transverse sections 
1 The sections as they came from the microtome were arranged in order on a large slide and 
mounted in glycerine in which they were kept indefinitely for further study. By this means the 
accuracy of the work is rendered just as great as with the similar paraffin series used for soft material. 
