54 BOTANICAL GAZETTE [july 



rays to become disintegrated not merely at their inner ends but 

 throughout their ontogenetic development is characteristic of many 

 tropical or subtropical species of Quercus. Severe, stunting types 

 of injuries hasten the disintegration of the sheets of ray tissue, 

 whereas stimulating or irritating injuries cause reversions to wide 

 multiseriate rays. 



Castanea dentata. — The common sweet chestnut illustrates a 

 case in which the reduction of multiseriate rays is nearly complete. 

 Vestiges of wide, multiseriate rays occur, however, in the first 

 formed tissue of very vigorous roots (figs, n and 20) and shoots 

 in the vicinity of the traces which pass out to the leaves and root- 

 lets. Multiseriate rays may also be recalled by stimulating types of 

 injuries such as are produced by the irritating effects of infections 

 of Endothia parasitica (fig. 16). It is interesting to note that not 

 only is the oak type of ray recalled but also the oak type of fiber- 

 tracheid and leaf (fig. 18). 



Betulaceae. — In the Betulaceae the reduction and disintegra- 

 tion of wide rays is far advanced. Typical wide multiseriate rays 

 occur, however, somewhat sporadically in the stems of Alnus thorn- 

 bijolia Nutt. and A. maritima, or may be recalled by stimulat- 

 ing injuries or vigorous growth in regions which do not normally 

 possess them. In most species the rays have become entirely dis- 

 integrated except in the peduncle, where narrow multiseriate rays 

 may be persistent. As the process of reduction is continued, these 

 sheets of dissected ray parenchyma are replaced gradually by aggre- 

 gations of multiseriate rays, and finally by bands of tissue that are 

 merely devoid of vessels. These trails or vestiges of former multi- 

 seriate rays, so-called false rays, are frequently persistent in the 

 vicinity of the traces of the leaves (fig. 12) and rootlets, and may 

 remain in these regions, particularly in the first annual ring of 

 vigorous roots and shoots, after they have disappeared from the 

 rest of the plant. This process of reduction is accelerated by 

 stunted, suppressed growth and retarded by vigor. The less 

 complete stages of reduction and disintegration are recalled by 

 stimulating injuries and unusually vigorous growth. 



We have seen above that the wide multiseriate rays of the 

 Fagales are characterized by a peculiar sclerenchymatous modifica- 



