219 
Notice of Book. 
It is already known that many of the Abietineae have medullary 
rays of complex structure, the wood-rays containing water-conducting 
tracheides, as well as living parenchymatous cells. On the other hand 
we also know that most Coniferae have bordered pits on the tangential 
surfaces of the latest formed autumn-wood. The author shows that 
the development of these two structures varies inversely. All Conifers 
which are destitute of tracheides in their rays, form tangential pits on 
their autumn-wood, while those in which the ray-tracheides are best 
developed, have few or no tangential pits. Both structures in fact 
serve the same purpose of providing a radial connection between the 
water-conducting tissues of successive annual rings. 
The author confirms Russow’s observation of the constant presence 
of intercellular spaces, containing air, between the elements of the 
rays, both in Gymnosperms and Dicotyledons. The living cells of the 
rays communicate by pits with these spaces, which are continuous 
through the cortical tissues with the lenticels or equivalent openings 
in the periderm. Thus the respiration of the deep-seated living 
elements of the wood is provided for. 
Among the most important of the author s discoveries is that of the 
physiological representatives of the companion-cells, in Gymnosperms, 
in w r hich these elements, as such, are never present. The chief con- 
clusions (some of which the author published in a previous paper) 
are here summed up as follows : (p. 55) 
In the Abietineae the functions of the companion-cells are fulfilled 
by certain rows of cells belonging to the medullary rays of the phloem. 
In a portion of the Cupressineae and Taxodineae these functions are 
divided between the specialized ray-cells and other series of elements 
forming part of the bast-parenchyma. In the remainder of these two 
tribes, and in the whole of the Taxineae and Araucarineae it is the 
bast-parenchyma alone which is concerned. In all these cases the 
function of the cells in question is inferred from their especially 
abundant protoplasmic contents, from the entire absence of starch 
when they are fully developed, from the fact that they reach maturity 
simultaneously with the sieve-tubes, and also become emptied and 
obliterated at the same time with them; lastly, from the fact that 
they are connected with the sieve-tubes by pits of peculiar structure, 
resembling one-sided sieve-plates. As regards the sieve-plates them- 
selves, the author decides that in the Coniferae they are never really 
open in the functional sieve-tube. The plug of swollen middle-lamella 
Q 
