2 I 2 
Review . 
in sharp contrast to that of the author, who regards the pith as con¬ 
stantly belonging to the extrastelar ground-tissue. There appears, 
however, to be no definite point in dispute between the two authors 
as to the facts of ontogeny, or (so far as this question is con¬ 
cerned) as to the probable course of evolution. The problem is 
perhaps an insoluble one, the answer depending on the point of 
view of the observer. Professor Jeffrey regards continuity, 
demarcation and histological similarity, as sufficient evidence of 
morphological identity ; Mr. Boodle relies rather on corresponding 
position of the tissues in related forms. 
On the other hand the question of reduction from concentric 
to collateral structure is a real and important one. Either the 
plants which now possess a “ medullated monostele ” are derived 
from ancestors with internal phloem or they are not. In the case 
of the Polypodiaceas there is good reason to think that the author’s 
hypothesis is the right one, and that cases of collateral structure 
in this family have really arisen by reduction. In other groups 
this is very doubtful, and in some (especially the fossil Lycopods) 
the evidence is all the other way. The impartial critic will pro¬ 
bably take the view that similar vascular structures have originated 
in different ways on various lines of descent, and that no one rigid 
scheme can be applied to all. Stages which can be seized “ in 
flagrante ” (p. 143) are not necessarily stages of degeneracy. 
The author’s division of Vascular Plants into Lycopsida 
(Lycopodiales and Equisetales) with ramular, but no foliar gaps in 
the stelar tube, and Pteropsida (Filicales and Phanerogams) in 
which foliar gaps are a constant feature, is already familiar to 
botanists and'needs no discussion. The distinction is no doubt a 
valuable one, and corresponds, in the opinion of the present writer, 
with natural affinities ; the relation of the Equisetal type of stele 
to that of the Lycopods requires, however, some further elucidation. 
The memoir is illustrated by six plates containing numerous 
figures, all from the author’s photographs. The illustrations are of 
great beauty, though perhaps a little more detail would sometimes 
have been welcome. 
In conclusion, Professor Jeffrey may be warmly congratulated 
on the completion of a solid and valuable contribution to the 
morphology of vegetable tissues, which, quite apart from our 
acceptance or otherwise of his theoretical conclusions, at once 
places him in the front rank of anatomical botanists. 
D. H. S, 
