244 Boodle and WorsdelL — On the 
subdivision by transverse walls in the cambium-segment, were 
given by Sanio 1 the special name of ‘ Ersatzfasern.’ Special 
cells are also set apart for storing up crystals of calcium 
oxalate ; these cells are distinguished by their small size, 
rectangular shape, and their arrangement in longitudinal 
rows ; they each contain usually a single crystal of about the 
same shape as the cell itself, sometimes, however, a cluster- 
crystal. All the elements thus far described belong to the 
concentric bands which are seen in transverse section (Figs. 
17, 28). The parenchyma-cells surrounding the vessels may 
vary in shape and size as do those in other parts of the 
wood ; but there is nothing abnormal about them. A cam- 
bium-segment has in most cases divided so as to form 
a vertical row of four parenchyma-cells ; the end-cells of 
these rows have often undergone slight sliding-growth, their 
pointed ends being intruded between surrounding cells. 
Where the walls of these elements border on a vessel, they 
are, of course, thickly covered with bordered pits ; when they 
abut on one another, however, the walls have simple pits 
(Fig. 16). 
The vessels , as seen in this section, vary considerably in 
appearance, both as regards size and the mode of perforation 
of their terminal walls ; these latter are always more or less 
oblique. In the primary wood, i.e. the first-formed after the 
protoxylem, the vessels are usually the narrowest, and as 
a rule become wider as they get farther out in the secondary 
wood. This plant is an instance of the occurrence in the 
wood of vessels with a single perforation, and of those with 
several perforations, with all transitions between the two. As 
a general rule, the typical vessels of the secondary wood 
possess wide cavities, and a single, large, round, or oval 
perforation in their terminal wall, which latter is more or less 
oblique, being inclined to the radial plane, so that its surface 
is clearly seen in a longitudinal radial section. The lateral 
walls of the vessel are thickly covered with bordered pits. 
Loc. cit., p. 96. 
