240 
C. C. FORSAITH 
found in the Salicales mentioned, the normal distribution was terminal, 
but vasicentric conditions were a feature of primitive regions. An 
application of the principles of comparative anatomy led to the con- 
clusion that the species of Salix and Populus with terminal parenchyma 
were derived by reduction from those which possessed vasicentric 
storage cells, and were, therefore, less primitive species (3). It will 
be shown later that terminal parenchyma in the Angiosperms, although 
not in the Conifers, is the result of reduction. 
The present article deals with conditions found in certain of the 
Malvales. 
Beginning with the Tiliaceae, figure i shows a transverse section of 
Tilia americana L. From this it appears that the wood elements are 
all thin walled, and the numerous clustered vessels are diffuse. The 
wood parenchyma is present as thin walled cells extending as tangential 
bands between the rays, which become broadened in the phloem 
region. In the upper portion of the figure alternate layers of hard 
and soft bast appear, of which the latter is composed of sieve tubes 
and storage cells. Figure 2 represents a tangential section of the same 
plant, showing one of the bands of parenchyma, the cells of which are 
indicated by thin-walled rectangular elements in the central portion of 
the illustration. A similar section through the first annual ring shows 
abundant diffuse parenchyma, which gradually becomes reduced to 
tangential bands in the later rings, shown in figure i. Figure 2 also 
represents the numerous diffuse vessels with abundant, spirally ar- 
ranged bordered pits and tertiary thickenings. However, no indica- 
tion of fusion of the pits to mere slits, a condition common in the Mal- 
vaceae and Sterculiaceae, was found. The two types of rays are 
similiar to those which Bailey (op. cit.) mentions in his studies of 
Betula, Carpinus, Ostrya, and Corylus. 
Figure 3 shows a transverse section of Hibiscus tiliaceus L. of the 
Malvaceae. Here the wood elements consist of bands of thick and 
thin-walled cells, alternately arranged between the two types of rays. 
The thin-walled portion is composed of clustered vessels and fibers, a 
condition very similar to that found in Tilia. This differs greatly 
from the thick-walled area, where the absence of vessels is conspicuous, 
and there is abundant diffuse parenchyma, which appears as thin- 
walled light and. dark cells. The dark appearance of certain cells 
represents the transverse wall of the wood parenchyma, in which simple 
pits may often be seen. Figure 4 illustrates a radial section of the same 
