6 
Chrysler .— The Nature of the Fertile Spike in 
vascular strand, and higher up joins again as shown in the figure ; but a new 
feature appears, in that half of the marginal strand remains with the main 
strand, while the other half passes out with the branch, which is accordingly 
C-shaped. The branch becomes concentric by acquiring an internal phloem 
as it passes out. In other specimens only the upper part of the marginal 
strand is present, that is, the part shown at the right-hand side of Fig. 20 ; 
following the series downward the marginal strand parts from the main 
strand (Fig. 20, right-hand side), swerves towards the edge of the latter but 
does not reach it, for it dwindles away and disappears. In other cases the 
marginal strand passes down only a short distance before it disappears, 
or its upper end may even be represented merely by a slight projection 
from the main strand. In such cases the branches which supply a group of 
sporangia appear to arise from the edge of the main strand. Since only the 
upper part of the marginal strand is present in these transitional cases, the 
strand can have no function ; its xylem cannot conduct water when it has 
Figs. 14-16. Diagrams illustrating the origin of the strands which supply the fertile spike in 
Botrych iiwi ternatum . 
no attachment below; hence it must be regarded as a vestigial structure, 
derived from the condition seen in all regions of the leaf of B. virginianum 
and in the fertile spike of some specimens of B. ternatum. This evidence 
plainly goes to support the view that B. virginianum has been derived from 
some less specialized fern, and that B. ternatum has been derived from 
some such plant as B. virginianum by a process of reduction in respect to 
the vascular system. The location of the internal phloem also supports 
this view. In most ferns this is present in both stem and leaf; in B. vir¬ 
ginianum it is absent from the stem but occurs in the leaf through most of 
its length ; in B. ternatum it is to be seen only in the remote branches 
of the leaf, especially in its fertile part; in other species its presence has 
not been recorded. It is becoming pretty well recognized that the leaf 
is one of the places where primitive features are apt to persist, and in 
the genus Botrychium we have a case where a structure is seen to gradually 
disappear from this organ. 
The two species B. ramosum (Roth), Aschers {B. matricariaefolium , 
A. Br.), and B. lanceolatum (S. G. Gmel.), Angs., are usually associated 
in schemes of classification, and the anatomical features bear this out. 
