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Notice of Book . 
a double purpose ; first, to supply the living elements themselves with 
water, and with certain salts, especially phosphates, which they can 
directly assimilate (p. 868) ; and further, to allow of the passage of or- 
ganic substances, especially carbohydrates, into the tracheae, by which 
they are rapidly conducted to the growing regions, at least during 
the spring (p. 894). 
The Vine is studied with special minuteness, and among many 
points of interest the author calls attention here to the emptying of 
the sieve-tubes and companion-cells in winter, a fact which is quite 
inconsistent with the function of food-reservoirs, attributed to these 
elements by Frank and Blass. 
The description of the wood of the Oak brings out a point of the 
highest morphological importance. The author regards the xylem 
generally as consisting primarily of two forms of tissue only — the 
tracheae and the parenchyma. In the great majority of woods the 
mechanical elements (fibres) belong to the parenchymatous system, 
as is indicated by their simple pits, and proved by the presence of 
transitional forms. In the Oak, however, and probably in all Cupu- 
liferae, as well as in Rosaceae and a few other cases, the so-called 
fibres have bordered pits, and pass over through intermediate forms 
into the tracheides. In these cases, in fact, the mechanical elements 
are homologous with the tracheal system, while in most woods they 
have arisen by modification of the parenchyma. This shows well how 
misleading a physiological classification of tissues may be from a 
morphological point of view. 
The author’s conclusions as to the wood are also extended to the 
bast. Here we have on the one hand the cribral system, to which 
the sieve-tubes and their companion-cells (if present) belong, and on 
the other the parenchymatous system, from the modification of which 
the bast-fibres have been derived. In the Gymnosperms, however, 
we have seen that the functional equivalents of the companion- 
cells belong to the parenchymatous system. Similar views of 
the morphology of the phloem had already been expressed by 
Lecomte. 
The phloem of Cucurbita has once more been fully investigated. 
Here also the author finds that the callus is derived directly from the 
protoplasm, its formation beginning in the pores of the sieve-plates. 
The function of the living protoplasmic layer lining the walls of the 
sieve-tubes consists, according to the author, in preventing diffusion 
