of Vascular Strands in A ngiopteris evecta. 397 
saceae investigated by him) as monostelic up to the formation 
of the first leaf. Above this an internal endodermis appears, 
and the arrangement becomes in consequence astelic, and, 
from the mode of grouping of the individual bundles, gamo- 
desmic. But in B. virginianum , according to Jeffrey 1 , the 
medulla is not separated from the xylem by an internal 
endodermis, and thus, to use the terminology of Van Tieghem, 
there is a perpetuation of the monostelic condition. That is, 
in closely related forms there exists a fundamental difference 
in the ‘ morphological structure ’ of their stems, as decided by 
the criterion of the endodermis. 
Perhaps, however, the best examples of its irregular dis- 
tribution are afforded by the Osmundaceae which have recently 
been investigated by Faull 2 . The stems of these Ferns are 
siphonostelic, the vascular tissue being arranged in a cylin- 
drical fashion round an axile pith. But it is only in one 
species, O. cinnamomea , that this pith is delimited by an endo- 
dermis from the vascular strand. It is on this ground that 
the Osmundaceae are held to be siphonostelic, and the 
absence of the endodermal criterion is looked on as a conse- 
quence of degeneration, a view which seeks support in the 
occasional presence of internal phloem (also confined to this 
species) which is, however, restricted to the regions where 
the stem is forking. We question the legitimacy of the argu- 
ment, and dissent from the conclusions as to degeneration. 
But we entirely agree with the author in the appropriateness 
of the term siphonostele as applicable to the vascular tissues 
of the stems of all these plants, though our reasons, as will 
have become apparent above, are not quite identical with 
his own. 
By thus emphasizing the vascular tissues as the feature of 
paramount importance, the pith is reduced to a subordinate 
position, similar to that which it occupied in the systems 
of De Bary and Sachs. But we become the gainers at least 
1 E. C. Jeffrey, The Gametophyte of Botrychium virginianum. Trans, of the 
Canadian Institute, v, pp. 283-4. 
2 Faull, The Anatomy of the Osmundaceae. Botanical Gazette, xxxii. 
