376 BOTANICAL GAZETTE . [NOVEMBER 
The writer has shown,’ by.a study of numerous species of 
Betulaceae and Fagaceae, that ample evidence of a compounding 
process exists in the rays of many living oaks, alders, birches, 
and hornbeams. Thus many American live oaks (fig. 5) possess 
bands of aggregated rays which are similar to the false rays of the 
Betulaceae. Among alders and birches species may be found 
with non-aggregated uniseriate rays, aggregated small rays, and 
large homogeneous rays like the so-called primary rays of oak. 
In fact, in the genus Alnus species may be found which form a 
perfect series of transitional steps between alders with non-aggre- 
gated uniseriate rays and Alnus rhombifolia Nutt., which often 
_ possesses large compound rays such as are found in the higher 
oaks. 
Further, Eames has shown that in the development of seedling 
oaks a similar series of stages occur. Thus in seedlings of Quercus 
alba L. and Q. rubra L., which in the adult possess broad homo- 
geneous rays, the first-formed wood resembles the adult wood of 
chestnut in possessing non-aggregated uniseriate rays. In the 
further growth of the young plant, aggregations of rays develop, 
which by subsequent fusion constitute the large rays of the mature 
wood, 
Thus three lines of evidence, afforded by the study of seedling 
stages, fossil ancestral forms, and the development of ray struc- 
tures in living forms, show conclusively that the wood of primitive 
_ Fagaceae and Betulaceae was characterized by the entire absence 
of large medullary rays. With the development of unequal 
seasonal temperatures, a highly organized storage system for foods 
became advantageous to plants, and the large rays of modern 
oaks have been evolved by an aggregation and fusion of numerous 
uniseriate rays to meet this demand. 
With these preliminary statements on the normal and ancestral 
features of oak wood, we may now turn to a more detailed consider- 
ation of the abnormal structures which exist in traumatic oaks. 
It has been pointed out above that traumatic regions are often 
the seat of ‘ancestral characters and show a series of stages similar 
8 Relation of the leaf trace to the origin and development of compound rays a 
the dicotyledons. Annals of Botany. JIned. 
