654 Bailey. The Evolutionary Hist or 



(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 pumila, 

 (L.) Mill, Castanopsis 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 



