44 BOTANICAL GAZETTE [july 



significant are the wide multiseriate rays which radiate from the 

 clusters of primary elements in the hypocotyledonary region of 

 young plants of Quercus virginiana Mill., a "live" or "evergreen" 

 oak which often possesses "aggregate" rays in the mature wood of 

 the stem. 



THE FIRST ANNUAL RING 



I 



The first elements formed by the cambium or lateral growing 

 point (the so-called first annual ring) have been considered by 

 Jeffrey, Thomson, and others to be conservative of ancestral 

 characters. It has been shown in the preceding pages that the 

 first formed portions of the seedling stem and root may possess 

 often only uniseriate rays which later appear to "aggregate" and 

 form wide sheets of ray tissue (figs. 4 and 6) . However, in certain 

 cases the first annual ring of vigorous shoots and roots may possess 

 "aggregate" and "multiseriate" rays when the mature portions 

 of these organs develop only uniseriate rays. For example, vestiges 

 of wide multiseriate rays have been observed in very vigorous young 

 roots of Castanea dentata (Marsh) Borkh. (figs. 11 and 20). These 

 rays occurred in the vicinity of the vascular strands which supply 

 the rootlets. Similarly, vestiges of "aggregate" rays occur in the 

 first formed portions of vigorous shoots and roots of Alnus mollis 



Fernald, Alnus acuminata H.B.K., and Ostrya virginiana (Mill.) 

 Koch, species which do not possess "aggregate" or "compound" 

 rays in the normal mature wood. 



The structure of vigorous mature shoots of Quercus velutina 

 and Q. rubra is also significant. As is well known, the primary 

 vascular bundles of the oak are not grouped about a more or less 

 cylindrical pith (except in the peduncle and epicotyledonary region), 

 but about one that is deeply fluted (figs. 9 and 10). In cross-section 

 the young twigs possess, therefore, a cambium layer that is com- 

 posed of ten alternating convex and concave arcs. Thus five 

 large wedge-shaped segments of secondary xylem are formed, 

 which include between them five narrow depressed segments with 

 more nearly parallel sides. This condition may persist in some 

 cases for a number of years, but usually is replaced sooner or later 

 by a stem of cylindrical outline. Vigorous shoots of the red and 



