ANATOMY 



463 



20. 



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 

 Ophidenna 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, 

 while those on the adaxial side pass out into 

 the fertile spike. The details are various : the 

 simplest is in the small O. Bergianum, where 

 the single leaf-trace strand may long remain 

 undivided, giving off two lateral strands which 

 fuse on the adaxial side to form the supply 

 for the spike : further up the strands of both 

 sterile lamina and of fertile spike may branch 

 again. In the larger species of Opliioglossum 

 the plan is the same, but with the difference 

 that the branching is more profuse, and takes 

 place before the lateral supply is given off 

 right and left for the fertile spike ; in the 

 larger species the latter consists not of a single 

 strand but of several. The same is the case 

 for O. pendulum, and even for O. palmatiiin 

 in the case of the lowest spike, though in the 

 upper spikes the supply is less regular in N . os - M-I? successive transverse 



" J sections of leaf of O. palmatwm, 



accordance with the indefinite positions which showing the origin of the vascuhu 



supply to the lowest of its spikes. 



they hold (Fig. 2=;Q, IA-I7). In OpMogloSSUm i7 = transverse section of the stalk of 



. . that spike. i8-23 = successive sections 



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



. the origin of the vascular supply to 



which frequently holds ItS Own throughout the second and third spikes. X 4 . 



the complicated reticulations of the expanded 



blade. In Botrycliium, 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 



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