Anatomy of Solenostelic Ferns. 709 
takes place varies from one leaf to another ; sometimes it 
breaks up almost immediately upon its departure from the 
stelar cylinder of the stem, and sometimes not until it has 
reached the free petiole (Fig. 17). While the leaf-trace 
remains a single continuous strand it has the form of a gutter 
with deeply incurved margins and a fold along each of its 
sides. After it has become broken up into separate portions 
these still keep the same conformation, so that some of 
the strands, chiefly those of the incurved margins, come 
to occupy a central position exactly as they do in Cyathea 
Brunonis. In this case, however, all the separate strands 
clearly arise from the leaf-gap margin, and from the leaf-gap 
margin only. 
It may be mentioned in passing that lateral shoots are of 
frequent occurrence in Dicksonia Barometz , and like those 
of Pteris elata they arise not from the margin but from the 
back of the leaf-trace, just before it begins to break up. 
Sometimes two may arise upon the same petiole. 
These observations all tend to prove that Trecul was quite 
correct in maintaining that the internal strands of the stem 
are strictly and essentially cauline, and this being granted, 
the idea is at once suggested that they are essentially similar 
in nature and origin to those of Dicksonia rubiginosa i Pteris 
elata y &c. It will be seen that this suggestion receives strong 
support from the manner in which the internal strands first 
appear in the young plant of Alsophila excelsa. 
I have been able to examine a number of young plants of 
Alsophila excelsa that were grown from the spore, and since 
the vascular system of the young plant of the Cyatheaceae 
has not yet been dealt with in detail, it is perhaps advisable 
to describe their structure at some length. Although the 
course of the development of the vascular system was 
practically the same in all the specimens examined, yet the 
rapidity with which the different stages are passed through 
varies considerably according to the conditions of growth. 
It must be understood, therefore, that the description given 
here is a more or less generalized one, and that it must not 
