354 
PROFESSOR W. WILLIAMSON ON THE ORGANIZATION 
sections, and fig'. 94, a, in vertical radial ones, whilst fig. 100 represents a portion of 
the radial section enlarged 1 5 diameters. The latter figure illustrates the way in which 
these cells are arranged, in long radial lines, most of the component cells of each of 
which are of exactly equal length, such groups constituting the peculiar limited clusters 
already referred to. The cells now present conspicuous examples of what has been 
termed “ prismatic parenchyma/’ As we approach the peripheral surface of the bark, we 
find the new and very characteristic conditions illustrated by the figures 93, 94, 95, and 
101. The outermost layer is seen to be an irregular parenchyma (fig. 93, b, 94, b), but 
even in this portion we again discover a tendency on the part of the cells to throw them- 
selves into groups, the component cells of which have evidently some common bond of 
union separating them from similar neighbouring groups ; but intermediate between this 
outer portion, b, and the prismatic cells, a, we find a curious arrangement. In fig. 93, 
some of the long contiguous parallel fines of prismatic cells gradually diverge in opposite 
directions, and allow of the intercalation of long, wedge-shaped rows of cells, c, c, whose 
longer division walls are again parallel to each other, and to the periphery of the bark 
as well as transverse to the radial direction of each individual wedge. On tracing these 
wedges inwards, i.e., towards the medullary surface of the bark, we find them to be 
continuous with one or two of the lines of prismatic cells, fig. 93, a. Hence it is clear 
that the one tissue stands in some definite relationship to the other. At their peripheral 
extremities these lines of parallel cells merge in those of the superficial parenchyma, b. 
On turning to the vertical radial section, fig. 94, we find that though in the transverse 
section, each of these wedges usually consists of but a single linear series of cells, in the 
radial vertical one it consists of several such series (fig. 94, c) superimposed vertically 
upon each other, and interposed between the separated layers of prismatic cells, fig. 94, 
ci, a. This section further reveals to us the fact that these cells are grouped in 
lenticular clusters, which form a part of the continuous series of such clusters seen 
in the prismatic tissue of the bark at fig. 94, a. The vertical partitions of the cells of 
each group, 94, c, are parallel to each other at the more internal parts of the bark, the 
cells having about the same dimensions as they possess in the transverse section, 
fig. 93, c, but as we approach the peripheral parenchyma, b, the cells of each cluster 
become shorter, broader, and less regular, assuming more and more the form of ordinary 
parenchyma. 
Fig. 95, which is a tangential section of the tissues under consideration, made along 
a line between the two stars of fig. 93, reveals a remarkable arrangement. We now 
find the prosenchymatous or prismatic cells forming a regular network, ct, a', enclosing 
numerous lenticular areas filled with parenchyma, fig. 95, c, c, and as the section has 
penetrated more deeply into the bark at a", than it has on the left hand portion 
of the figure, we see that these parenchymatous areas become gradually smaller 
(fig. 95, c, c), and finally almost disappear, the cells merging in the mass of prismatic 
tissue, a". It thus appears that the cells seen in fig. 93, 94, and 95, c, are really tabular 
cells whose broad parallel sides are parallel to the surface of the bark, whilst them 
