432 
CARL S. HOAR 
that in the genus Betula the phenomenon of aggregation of rays is a 
primitive condition persisting with the diffuse type in Betula popuU- 
folia, but in other species confined more or less definitely to primitive 
organs and regions or recalled only as a result of injury. 
In a recent article an attempt has been made to discredit the aggre- 
gate ray as the precursor of the conditions of ray structure obtaining 
in the mass of arboreal Dicotyledons (Bailey and Sinnott, 1914). In 
the present connection it can only be emphasized that the conclusions 
which are logically drawn from the facts must be in accord with the 
general principles established as a result of the comparison of fossil 
(Mesozoic and Paleozoic) Gymnosperms with those still living. It is 
(Certain from these studies that ancestral conditions persist strongly in 
reproductive structures and in roots, and that they may be present in 
the earlier rings of growth of the vegetative stem even when absent in 
the mature wood. Further, they often reappear in response to injury 
or abnormal situations. Applying these principles to the Betulaceae 
from Alnus to Betula, beyond reasonable question the phenomenon of 
aggregation of rays is primitive for the family. The genus Alnus 
illustrates this type in a primitive condition. In the higher genera, 
Carpinus, Ostrya and Betula, it has given place to the diffuse state 
resulting from the lateral spreading of the original congeries or aggre- 
gations of rays; but in these genera the ancestral condition often 
persists in conservative organs and regions or may return as a conse- 
quence of injury. If the principles here cited are sound and the con- 
clusions drawn are logical, the criticism above referred to appears to 
have very slight value. 
It seems clear that the anatomy of the cohort, of which the Betu- 
laceae form one member, is distinctly that of a low group. The 
presence of parenchyma distributed throughout the entire annual 
ring is a feature not usually found in the higher Dicotyledons. The 
vessels, also, with their characteristically scalariform perforations are 
unquestionably of a primitive nature. The fibers are in general 
fiber-tracheids, and above all, the rays show features of organization 
which are common to the lower families of Angiosperms and to the 
highest Gymnosperms. With these facts in view, it is obviously 
impossible to assign this family to a very high position. 
