428 
CARL S. HOAR 
The genus Cory'us is characterized by having aggregate rays 
throughout the entire stem. Figure lo is a section of the root of 
Corylus americana Walt, cut through the region of the root-trace. 
It will be not ced that around the trace the rays are aggregated. 
Figure ii is that of a longitudinal section of Corylus rostrata Ait. 
taken just below the root-trace. Only ray cells and tracheids with 
wood parenchyma cells appear extending through the center. It is 
the aggregate type which is formed about the leaf-trace or the root- 
trace. The genus Corylus is thus characterized by having the aggre- 
gate type of ray well developed in both root and stem. 
In the genus Carpinus the situation is comparable to that of 
Corylus. Figure 12 is that of a transverse section of Carpinus cordata 
cut near the region of the leaf-trace. The rays are here clustered into 
more or less definite congeries in which the vessels are very scarce. 
In other words, the wood normally has rays in the aggregate condition. 
In figure 13, a transverse view of the root of the same species, the rays 
are in general diffuse but aggregated in relation to the root-trace. 
Figure 14 is a greater magnification of a portion of figure 13 showing 
more distinctly the area directly around the root-trace and better 
illustrating the same characteristics. 
In the case of Ostrya the normal stem does not have the rays dis- 
tinctly aggregated, but instead they are more or less scattered. Never- 
theless, as figure 15 indicates, the aggregate condition is somewhat 
clearly shown in regions near the pith. This is another example of the 
retention of ancestral characters in the first annual ring. Figure 16, 
a transverse section of a root of Ostrya virginia?ia Mill., illustrates 
aggregation (bottom of the figure) and absence of this phenomenon in 
the rest of the periphery. Figure 17, a higher magnification of the 
lower part of the preceding photograph, shows the aggregate ray 
developed in relation to a secondary root. Here may be seen mani- 
fested the characteristics of aggregation; namely, the clustering of 
rays with the exclusion of vessels. The root, most conservative of 
plant organs, naturally reproduces the primitive condition, aggregation 
of rays in the vicinity of the appendages. In the stem, contrariwise, 
we have to do with the most progressive and variable of organs and 
as a consequence we are not surprised to discover the absence of aggre- 
gate rays in its mature structure. Vestiges of these, however, occur, 
as shown in figure 15, in the earlier annual rings and nearer the pith. 
In other words, the stem of Ostrya virginiana has passed through the 
