Reviezv. 
2 11 
The close agreement in structure between Lyginodendron and 
Heteranginm (a genus somewhat summarily dismissed by our author) 
points clearly to the direct derivation of the medullated structure 
of the former from the protostele of the latter type, while the 
hypothetical intercalation of a concentric, Medullosa-Wke stage, 
appears gratuitous and unsupported by evidence; no Medullosa is 
known which is in any way intermediate between the types of 
structure represented by Heteranginm and Lyginodendron. 
The comparison drawn by previous writers between the stelar 
structure of Osmunda and that of Lyginodendron is accepted by the 
author, and regarded as supporting his views. He says: “Thelate 
Professor Huxley considered that in the almost complete geological 
sequence from the pentadactyl early horses to the monodactyl 
horses of the present day, existed one of the strongest proofs in 
favour of the general principle of evolution by reduction and 
specialization. We find apparently a similar series of reduction 
and specialization in the Osmundaceae which may be applied to the 
elucidation of the general problem of the evolution of the central 
cylinder in the higher plants ” (p. 137). The hypothesis of reduction 
in the Osmundaceae appears, however, too uncertain at present to 
be employed with safety in elucidation of the structure of other 
groups. 
In his concluding paragraphs the author sums up the morpho¬ 
logical and phylogenetic results of his work. He criticises the 
views of Strasburger as to the endodermis. That author, as is 
well known, has drawn a distinction between the “ phloeotci ma” 
or innermost layer of the cortex, and the endodermis, a layer 
characterized by its histological structure, which may or may 
not happen to coincide with the phloeoterma. Professor Jeffrey 
appears to treat the two conceptions as identical—wherever he 
finds a layer of cells with endodermal characters he considers it 
as fixing the limit between fundamental and vascular tissues. In a 
physiological sense this, no doubt, holds good very widely; the 
author, however, makes light of the physiological function of the 
endodermis (though that it must have some function seems obvious). 
The idea of the morphological value of the endodermis appears to 
have arisen from the fact of its coinciding, in certain cases (notably 
in the root) with histogenetic boundaries, and would therefore seem 
to stand or fall with the doctrine of histogenetic zones, a subject 
too wide to be entered on here. 
Mr. Boodle’s view that the pith always forms part of the stele, 
irrespective of the distribution of the endodermal sheaths, stands 
