ANATOMY 



463 



system of the axis : comparison with the Ferns shows that in them the 

 concrete leaf-trace is characteristic of the primitive types, and that its 

 separation into many distinct strands is a feature of those which are later 

 and derivative. This analogy strongly supports 

 the view that the state of the leaf-trace in 

 >j Ophiderma is not primitive. 



Passing up the petiole the vascular strands 

 undergo branchings, which vary in extent 

 according to the dimensions of the fully formed 

 leaf. The strands arrange themselves in an 

 approximate circle in the transverse section, 

 lile those on the adaxial side pass out into 

 ic fertile spike. The details are various : the 

 iplest is in the small O. Bergianum, where 

 ic single leaf-trace strand may long remain 

 idivided, giving off two lateral strands which 

 ise on the adaxial side to form the supply 

 >r the spike : further up the strands of both 

 jrile lamina and of fertile spike may branch 

 tin. In the larger species of Ophioglossum 

 ic plan is the same, but with the difference 

 it the branching is more profuse, and takes 

 lace before the lateral supply is given off 

 right and left for the fertile spike ; in the 

 rger species the latter consists not of a single 

 ind but of several. The same is the case 

 O. pendulum, and even for O. palmatum 

 the case of the lowest spike, though in the FlG - 2 59- 



ipper spikes the supply is less regular in N . os - J 4-i6 successive transverse 



. * sections of leaf of O. palmatum, 



ordance with the indefinite positions which showing the origin of the vascular 



supply to the lowest of its spikes. 



y hold (Fig. 259, 14-17). In OphiogloSSUm 17 = transverse section of the stalk of 



that spike. 18-23 = successive sections 



re is a strong median strand in the leaf, higher up on the same leaf, showing 



.. iii-i- tne origin of the vascular supply to 



frequently holds itS OWn throughout the second and third spikes. X 4 . 



ie complicated reticulations of the expanded 



blade. In Botrychium, however, the broad strap-shaped leaf-trace forks 

 early; and from the adaxial margins of each limb branch-strands are 

 given off, which form the supply of the fertile spike : subsequently 

 both systems may branch further, showing dichotomous characters, and an 

 ultimate " Neuropteris " venation. In Helminthostachys the first branchings 

 of the leaf-strand are described as dichotomous ; the resulting strands 

 arrange themselves in a ring, and traverse the petiole with occasional 

 anastomoses. Where the leaf branches complex anastomoses occur, 

 resulting in a fairly regular vascular supply passing into each branch. 

 The spike receives four or five strands, arranged in a circle, in its 

 transverse section. Further branchings occur in both sterile and fertile 



