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 

 shoot with its appendages. With this view of the general Equisetal 

 morphology the development of the embryo of Etfiiisetum 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. 



