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Notice of Book . 
by which the continuity of the protoplasm is interrupted, does not, he 
believes, offer any hindrance to the passage of dissolved substances, 
though it renders the transference of living protoplasm impossible. 
The callus is stated to be formed directly from the protoplasm ; it 
is regarded as a by-product, rather than a reserve- substance ; in some 
cases it becomes of functional importance as effecting the temporary 
closure of the sieve-pit. 
The arrangement, both of the true companion-cells in Angiosperms, 
and of their representatives in Gymnosperms, shows that they cannot 
serve for the longitudinal conduction of food-substances. Their function 
is rather to receive the albuminous material conveyed by the sieve- 
tubes, and ultimately to pass it on to developing tissues. 
The author finds that the arrangement of the sclerenchymatous 
elements in the bast of most Conifers is such as to exclude the possi- 
bility of mechanical function. In such cases these elements are 
regarded as serving simply for the deposition of excessive cellulose, 
formed as a necessary result of metabolic processes in the starch- 
containing cells (p. 77). It is difficult to believe in so great a waste 
of carbohydrate material, and some local mechanical use (e. g. the 
hardening of the bark) may perhaps be conjectured. 
Prof. Strasburger points out that the primary structure of the phloem 
in Abietineae resembles the permanent structure in Araucarineae and 
Taxineae. This anatomical fact, in connection with other morpho- 
logical points, and with the results of Palaeontology, leads the author 
to regard the two latter families as relatively primitive forms, and the 
Abietineae as the most modified group of Conifers. 
The careful re-investigation of the leaves of Coniferae has led to 
some interesting results, of which the most important is perhaps the 
discovery of ‘ albuminous cells’ forming an extension of the phloem of 
the leaf-bundles, just as the transfusion-tracheides form an extension of 
their xylem. These albuminous cells no doubt have the same function as 
the terminal phloem-elements of the fine branches of the bundle-system 
in Angiospermous leaves. In both cases this function is to absorb 
from the mesophyll the nitrogenous products of assimilation, which 
are destined to be conducted elsewhere by the sieve-tubes. 
In Ptnus the central-cylinder of the leaf is alone continuous with the 
stem. Hence all the assimilated food must pass through the tissues 
of the cylinder (vascular bundles and conjunctive parenchyma). This 
observation leads to a general discussion of the internal morphology 
