SUMMARY 397 
original shoot. The appendages spring laterally below the apex of the 
axis, but even in extreme types they never attain to very great dimensions. 
An interesting point is the dichotomous branching of the leaf in early 
forms: this is important for comparison with other phyla, and will have 
its place especially in the comparative morphology of the strobili. 
It is possible to account for even the most complex types of the 
Equisetales as resulting from advances along the lines of ramification and 
of progressive sterilisation above indicated, but starting from the simple 
shopt with its appendages. With this view of the general Equisetal 
morphology the development of the embryo of Lgutsetum coincides, the 
axis taking the lead from the first, while the variability of position of the 
first root is a further indication of its accessory character. Finally, 
the vascular anatomy, so long held to be Phanerogamic in its character 
rather than Pteridophytic, is now shown to be referable in origin to a 
primitive monostele: the structure in the known forms is far removed, it 
is true, from the condition of a solid xylem-core; but it has been shown 
that the structure of the xylem that remains is clearly indicative of origin 
from a primitive type of monostele. These characters taken collectively 
point in no uncertain way to a strobiloid origin of the Equisetal 
sporophyte. 
