i3° 
Notice of Book . 
The first part of the subject examined is the sliding growth in the 
transverse direction, which occurs during the formation of the vessels 
of the xylem. Attention is chiefly directed to the vessels of the 
secondary wood of Dicotyledons, as here the regularity of the radial 
arrangement of the cambial cells and their immediate derivatives 
renders it comparatively easy to follow the subsequent displacements. 
In the first instance the growth of the developing vessel in the 
tangential direction is considered. The author proves that the 
tangential extension of the cambial zone as a whole, during the 
development of any one vessel, is so insignificant that it may be left 
out of consideration. 
The exact description of the tangential growth of the young vessels 
would not be intelligible in all its details without reference to the 
author’s figures. It is shown, however, that the extension which 
these elements undergo cannot be accounted for in any other way 
than by the hypothesis of sliding growth between the vessel and the 
cells of the neighbouring radial rows. Three other possibilities are here 
discussed ; of these only one is sufficiently probable to need mention 
here, namely, that the vessel in its growth simply compresses and 
obliterates certain of the adjacent cells. According to Dr. Krabbe’s 
observations such obliteration takes place very rarely, a statement with 
which those who are familiar with transverse sections of wood will 
probably agree. 
The facts to be accounted for are : that the vessel increases in 
diameter ; that it is in contact with more numerous cells when mature 
than it was at its first origin, and that the radial rows of cells 
adjoining the vessel on either side become interrupted by its tan- 
gential extension. This penetration of the growing vessel between 
the adjacent cells is shown by careful measurements to involve sliding 
growth between the growing portion of the wall of the vessel, on the 
one hand, and the walls of the cells, between which it penetrates, on 
the other. In cases where larger vessels are formed this tangential 
growth may extend through several radial rows. In describing these 
phenomena the author points out that they cannot be explained with- 
out supposing that each cell has a distinct membrance of its own, — a 
point which does not admit of direct microscopic demonstration at so 
early a stage. 
It is shown that the tangential growth of the vessel is only possible 
so long as the tissue to which it belongs is undergoing extension in 
