in the ‘ Seedlings ’ of Certain Leptosporangiate Ferns. 407 
‘ persisted ’ through successive internodes, and is only occasionally in 
continuity with the external ground-tissue at the gaps. That is to say, 
the structure occurring in O. cinnamomea is very closely akin to that 
of solenostelic ferns, the absence of internal phloem being the chief 
difference, while the resemblance to Platyzoma microphyllum 1 is even 
more striking. 
If the above contention should ultimately prove correct, it would 
have an important bearing upon the relative primitiveness of the different 
types of vascular organization occurring in the Osmundaceae. Faull 
believes that O. cinnamomea and O. Claytoniana stand at opposite ends 
of a series, with O. regalis as an intermediate form. Strictly speaking, 
there is no essential difference between the vascular systems of O. regalis 
and O . Claytoniana , and hence, for the purpose of comparison, they may be 
regarded as the same. Of this series Faull regards O. cinnamomea as 
the more primitive, i. e. least modified from the amphiphloic siphonostelic 
type, and derived from the siphonostele by ‘ degeneration/ From this 
it follows that O . regalis and O. Claytoniana have still further de- 
generated. 
This position has already been subjected to criticism at the hands of 
Boodle, and, as a result of the present work, the writer is inclined to take 
a diametrically opposite view of the question. Admitting that a complete 
knowledge of the young vascular system in the Osmundaceae is urgently 
needed, he believes that comparison with other and fully-known types 
points to the conclusion that the type of vascular organization possessed by 
O. regalis and O. Claytonia7ia is that which is more primitive, and that 
the vascular system of O. cinnamomea , instead of being the result of 
degeneration, is, so to speak, really on the up-grade, and has, indeed, 
advanced a considerable distanee along the phylogenetic road which 
at the present time leads to dictyostely. 
The structure of O. regalis and O. Claytoniana can be plausibly 
explained if compared with the young vascular system of a Polypodiaceous 
fern. The earlier leaf-traces of the latter involve the differentiation of 
no real leaf-gaps — we have merely the xylem discontinuous at a certain 
point, and the external and internal phloem more or less continuous 
between the horns of the xylem. Now, if we consider a plant in which 
the internal potential vascular tissue does not assume the definite 
characters of phloem (and this is merely assuming the persistence of 
the earliest condition of a dictyostelic vascular system) 2 , then this first 
‘ leaf-gap ’ corresponds to a ‘ medullary ray ’ of Osmunda . If, further, we 
suppose the first and succeeding leaf-gaps to remain unclosed, we have 
a structure exactly resembling that found in mature plants of Osmunda 
1 Boodle, Comparative anatomy of the Hymenophyllaceae, Schizaeaceae, and Gleicheniaceae. 
III. Gleicheniaceae. Annals of Botany, xv. 2 Cf. Angiopteris evecta. 
