1914] BAILEY &• SINNOTT—PHYLOGENY OF ANGIOSPERMS 51 



twig of Fagus grandifolia, since the gaps which separate the numer- 

 ous distinct clusters of protoxylem subtend an equal number of 

 multiseriate rays. There is this difference, however, that in sub- 

 sequent growth of the twigs not all of these rays increase in breadth, 

 as do those of the vigorous seedling stem and peduncle. The multi- 

 seriate rays which occur in the first annual layer of growth of the- 



narrow depressed segments (fig. 9) gradually decrease in width 



during the next two years' growth and become uniseriate. That 

 these rays are vestiges of wide rays which have been reduced by 

 the arrested development of the depressed segments is indicated 

 by the fact that when the cambium loses its specialized lobed form 

 and releases these segments, one or more of the rays may eventually 

 increase in width from uniseriate to multiseriate. In addition, 

 it is interesting to note that a stimulating type of injury causes 

 these reduced rays to resume their multiseriate form. 



The "secondary" multiseriate rays which are formed as the 

 stem increases in circumference are wider and arise more abruptly 

 than do those of the beech. These rays may be formed by the 

 rapid widening of a simple uniseriate ray or may show indications 

 of incipient retardation of development and be disintegrated slightly 

 at their inner ends. 



The reduction of multiseriate rays is conspicuous in feeble, 

 poorly nourished seedlings or in stunted or suppressed twigs (figs. 

 4 and 10). Under such conditions of reduced vitality the first 

 formed portions of the seedling plant may possess only uniseriate 

 rays, although the outlines of the suppressed wide rays are clearly 

 marked; for each gap between the primary vascular bundles sub- 

 tends an aggregation of uniseriate rays or a band of tissue that is 

 entirely devoid of vessels. These " trails," or so-called "false" 

 ra ys, radiate outward and in turn subtend the multiseriate rays 

 which are eventually formed during subsequent growth. The 

 retarded development of "secondary" multiseriate rays is likewise 

 m arked by a trail of aggregated small rays and tissue devoid of 

 tracheae. If the cambium of a feeble seedling receives a stimulating 

 injury or suddenly increases in vigor, multiseriate rays are recalled 

 at once and appear abruptly in those radii from which they have 

 been lost. 



