65 1 
Foliar Ray in the Wood of the Dicotyledons. 
in primitive parts, e. g. the seedling. In passing from these regions to 
subsequently formed portions of the stem the development of the foliar ray 
tissue is a progression in the direction of compounding. The significant 
facts to be kept in mind are that in Quercus the first-formed wood of the 
seedling possesses solely uniseriate rays, the development of foliar rays 
is a progression in the direction of compounding, and more primitive stages 
of the 4 linking-up ’ process occur in the young plant. The 4 linking up of 
small rays to form large ones in the first rings of the twigs of Quercus 
Rohur 5 does not invalidate seedling evidence, since in this species the 
solidifying of the foliar ray may not have worked back to the region of the 
pith in the early wood of the stem and branches. 
An unfortunate difficulty has been introduced by Professor Groom : 
that the broad solid ray may be primitive in oak, since it apparently under- 
goes subdivision in many cases. In view of the progression in the direction 
of compounding which occurs in the development of ray structures in the 
life-history of oak, alder, and other genera of the Fagales it is difficult for 
the writer to concur in this turning of the foliar compound ray inside out. 
That the foliar ray is dissected into shallower sheets of ray tissue in passing 
horizontally from the young to the older portions of a thick stem is true 
for all species of the Fagales. This is as true for species in which foliar 
rays are of the aggregating type as for those higher types in which nearly 
homogeneous masses of fused ray tissue are related to the traces of the 
leaves. In 4 exogenous ’ stems which are increasing rapidly in circumference 
a multiplication of elements, fibres, vessels, parenchyma, and rays must 
occur with added layers of growth. Therefore the dissection of foliar rays 
is essential to maintain the proper proportion of ray tissue in the older 
zones of the stem. However, the impulse which produces this dissection 
of foliar rays is fundamentally different from that which results in the 
evolution of storage tissue in relation to the traces of the leaves, and cannot 
be considered evidence for believing that the broad, solid type of ray is 
primitive in Quercus. Both phenomena are often active in the same foliar 
ray. For example, in Alnus rhombifolia , Quercus virginiana , Mill, or 
Q. densiflora , Hook, and Arn., foliar rays of the aggregate type are gradually 
4 built up ’ in passing from the vicinity of the leaf-trace to the mature 
portion of a wide stem, yet a dissection of this aggregating mass of tissue 
takes place in the older wood, resulting in the formation of 4 lower ’ and 
more numerous sheets of compounding tissue. 
In this connexion Professor Groom’s conclusions in regard to 4 Quercus 
( Pasania ) fenestrata (Q. spicata) ’ are of interest : 4 In Q. fenestrata these 
characteristic high rays are often approximated in pairs, and between the 
two rays forming a pair the boundary of the annual ring is much nearer the 
centre of the stem than it is elsewhere (PL LXXXV, Fig. is). Moreover, 
the space between the two rays forming a pair is devoid of vessels. These 
