224 
Notice of Book. 
secondary growth of the roots of these plants are recorded, some 
of which, however, were anticipated in the first edition of the author’s 
‘ Practicum.’ 
The anatomy of vascular Cryptogams is disposed of rather rapidly. 
As regards Equisetum a new interpretation of the structure of the 
bundle is given. It is also proved that here, as in Grasses, the inter- 
cellular space accompanying the xylem is always filled with water, not 
with air, even in those species in which each bundle is enclosed within 
an endodermis of its own. 
Van Tieghem’s interpretation of the prevailing structure of the stem 
in Ferns as ‘ polystelic ’ (each 4 concentric bundle ’ of De Bary represent- 
ing an entire cylinder like that of a root), is adopted by the author, 
who, however, differs from the French anatomist as to the morphology 
of the phloem-sheath. This layer is regarded by Prof. Strasburger 
as constantly belonging to the cortex, while Van Tieghem finds that 
in many Ferns it is the homologue of the pericycle. That the phloem- 
sheath and endodermis are often sister-layers is certain, but it is pos- 
sible that in these cases both layers may belong to the cylinder, as was 
suggested by J. E. Weiss. These difficulties of delimitation occur in 
all morphological questions, and no doubt the problem is often in- 
soluble. 
In many Ferns the tracheides form a thick and uniform strand, in 
which no living cells are interposed, so that here at any rate there 
is no room for the vitalistic theory of water-conduction. 
The central cylinder of Lycopodium is regarded as 4 gamostelic,’ 
in Van Tieghem’s sense, i. e. as representing a fusion of a number of 
4 steles ’ like those of Selaginella. This view does not appear to rest 
on any sufficient developmental or comparative evidence, though as 
a mere description of the mature structure it is appropriate enough. 
The author devotes a chapter to a summary of his anatomical 
results, but this has been to a great extent anticipated in our survey. 
We have already called attention to the adoption of the general 
anatomical conceptions of Van Tieghem. It is unnecessary here to 
follow the discussions which have arisen between the two investigators 
on points of detail. The idea of the cylinder or stele as a primary 
anatomical region, superior to the vascular bundles, appears to the 
reviewer to be a fruitful one, chiefly for two reasons. First, it enables 
us to understand the homologies between root and stem, which were 
to a great extent obscured by De Bary’s treatment of the central- 
