654 Bailey.— The Evolutionary History of the 
(Marsh) Borkh. It will be observed that the wood is characterized by the 
primitive type of ray structure. A similar condition is found to exist in other 
members of the Cupuliferae. Thus the mature wood of Castanea ptimila , 
(L.) Mill, Cctstanopsis hystrix , A. DC., C. Indica , A. DC., Alnus acuminata , 
H.K.B., A. mollis , Fernald, A. yasha, Matsum, &c., possess characteristically 
only uniseriate rays. In view of the fact that the first-formed wood 
of primitive Dicotyledonous plants possesses only uniseriate rays and the 
foliar ray has been ‘ built up ’ from congeries of small rays, it might 
naturally be supposed that the plants under consideration possessed the 
primitive type of Dicotyledonous wood from which have been evolved the 
higher and more complex forms. However, before accepting this supposition 
as a correct one, a more detailed examination of their structure is necessary. 
The fallacy of inferring that less complex plants are of necessity more 
primitive has in recent years been clearly illustrated by the study of the 
comparative anatomy of living and fossil plants. The pines, which, owing 
to their complex structure, have been commonly considered the most 
recent of Coniferous plants, have been shown to be very old geologically, 
and the supposedly primitive Cupressineae are now known to be of com- 
paratively recent origin, and to have been evolved from more complex 
ancestors. In other words, in the evolution of living plants may be traced 
the gradual reduction and disappearance, as well as the origin and develop- 
ment, of specialized tissues. Among Coniferous plants the reduction of resin 
canals and ray tracheides can be observed in the Abieteae, Cupressineae, 
and Taxodineae, as well as the evolution of ray tracheides and wood 
parenchyma in the Pineae. Similarly, among Araucarian plants there 
exists the reduction of resin canals and Abietineous pitting. It is, there- 
fore, to be expected that among living Dicotyledons reduced forms occur 
with less complex structures than those of more primitive forms from which 
they have been derived, and an examination of those regions which are 
known to retain ancestral characters is essential in determining their real 
phylogenetic position. 
First-formed Wood of Vigorous Mature Twigs. 
In Fig. 4 is illustrated the cross-section of a vigorous mature shoot of 
Alnus mollis. It will be observed that in the first annual ring are 
numerous large rays of the foliar type. These rays gradually die out 
in the second and third annual layers of growth, and the wood of the 
older portion of the twig possesses only the uniseriate rays characteristic 
of the mature wood of the species. In the first annual ring of twigs of 
normal growth the large rays are absent and the wood resembles that 
of the mature stem. Since the phylogenetic importance of the first 
annual ring of vigorous branches of plants which have suffered vegetative 
reduction has been pointed out by Jeffrey (7) in the recapitulation of resin 
