314 BOTANICAL GAZETTE [APRIL 
this particular theory and asserts that the great factor at work 
in the formation of the compound ray is the influence of the leat 
trace. Since the stem adjacent to the leaf trace is the most natural 
storage place for food manufactured in the leaf, he concludes that 
the storage organs, the rays, would be enormously developed at 
this particular point in the stem for the purpose of storing assimi- 
lates descending from the large persistent leaves of Mesozoic 
angiosperms. Following its formation at the leaf trace, the broad 
ray has spread throughout the tree. These ‘“‘foliar’’ rays, as BAILEY 
calls them, have persisted in the families of the dicotyledons either 
in their very primitive “aggregate” condition (composed of 
congeries of small rays) or in their more advanced “compound”’ 
condition (completely parenchymatous). 
A second line of evidence which amplifies this original hypothesis 
is advanced by THompson (8). He maintains that the “multi- 
seriate’’ type of ray has originated from the diffused portions of 
“aggregate” or ‘‘compound” rays. With the advent of a severe 
winter season and the consequent acquirement of the deciduous 
habit by the leaves, the organization of storage systems about the 
leaf trace was no longer of advantage. Thus in the development of 
the multiseriate ray, which characterizes the majority of living 
dicotyledons, portions of the aggregate or compound rays have been 
diffused more or less uniformly throughout the stem. 
In opposition to the aggregate ray hypothesis, BAILEY and 
Srnnotr (4) in a more recent article suggest the possibility that the 
clusters of small rays may be, in many cases, stages in the breaking 
down rather than the building up of wide rays. They state that 
the multiseriate ray has originated merely by the gradual increase 
in width of the primitive uniseriate ray, and that in all probability 
the so-called “aggregate” rays, instead of being formed by the 
fusion of many smaller linear rays, are merely stages in the reduction 
and disintegration of the wide multiseriate rays. 
Material and methods 
About January 1, 1916, specimens of white oak twigs vary ing 
in age from 1 to 19 years were collected from three different trees 
on the campus of Oberlin College and from three different regions 
