221 
Notice of Book. 
of stem and leaf, which is of fundamental importance. All the parts 
of the central cylinder of the leaf in Pinus are continuous with the 
corresponding tissues of the stem, and ultimately with those of the 
root. It follows (p. in) that in Pinus two tissue-systems, that of the 
central-cylinder and that of the primary cortex, run separately through- 
out the entire plant. This morphological separation coincides on the 
whole with distinctness of function. The cortical tissue is the great 
assimilating system ; the central-cylinder assumes the function of 
conduction. ‘ As it is in Pinus , so is it in essentials in all vascular 
plants, while the distribution of the two tissue-systems in the plants, 
and their mutual delimitation, are also facts of general application.’ 
Thus the point of view of the French anatomist Van Tieghem is 
definitely adopted by the chief German authority ; the central-cylinder 
is recognised as an anatomical region of the first order, of which the 
vascular bundles are subordinate parts. The importance of this con- 
ception, which profoundly modifies the anatomical teaching of Sachs 
and De Bary, is evident all through the book. 
A section on the vegetative structure of Gnetaceae brings out the 
general agreement with Dicotyledons rather than with Gymnosperms. 
The chief anatomical characters which indicate the true gymno- 
spermous affinities, are to be found in the structure of the phloem, 
and in the indications of transfusion tissue in the leaves. 
The investigation of the Cycadeae has not yielded much which is 
new. The structure of the phloem is that of the simpler Coniferae. 
The anatomy of a large number of dicotyledonous types is described 
in the fullest detail. The value of these minute researches can scarcely 
be fully appreciated except by those who are themselves engaged in 
such investigations, a remark which applies in a great degree to the 
whole book. The wood of Dicotyledons turns out to be even more 
complicated than was supposed before. In many of these plants, for 
example (e.g.Salix), both the medullary rays and the xylem-parenchyma 
consist of two kinds of cells. In the case of the rays they may be 
distinguished as horizontal and vertical cells. The former contain 
abundant starch, and communicate by pits with the intercellular 
spaces, but not with the vessels ; the latter are destitute of starch in 
summer, and are in communication with the vessels, but not with 
the intercellular spaces. The former serve chiefly for the conduction 
of assimilated substances, and for gaseous interchange ; the latter 
communicate with the tracheal system. This communication serves 
