50 BOTANICAL GAZETTE [July 



annual layer of growth, therefore, there are rays one to many cells 

 wide. In the first annual ring the widest rays occur in the vicinity 

 of the nodes, on each side of traces which are about to enter the 

 leaves. 



and development 



fundamentally the same 



mature stem. The root (fig. 2), which is comm 



from the five 



protoxylem. These rays are high and connect the traces 



of the rootlets. 



formed 



rapidly and at the same time are dissected into shallower sheets of 

 parenchymatous tissue. The other radii of the root possess at 

 first only uniseriate rays, certain of which later increase in width 

 as do some of the linear rays of the stem. Conditions such as have 

 just been described occur in shoots and roots of normal development. 

 The structure of wide rays is often different in suppressed, stunted, 

 or feeble growth. Under these circumstances the first rays formed 



cambium 



and rootlets, where multiseriate 



stem 



ma at their 



In the root and the hypocotyledonary region, however, where the 

 rays are often of considerable width, the reduction may be accom- 

 panied by slight indications of disintegration or dissection. If a 

 shoot or root of this type receives a stimulating injury or develops 

 suddenly a more normal type of vigor, an abrupt transition from 

 uniseriate to wide multiseriate rays takes place, so that arcs of the 

 cambium that have been forming linear rays and tracheary ele- 

 ments suddenly form only ray parenchyma (fig. k) . The phloem 



multiseriate 



stem 



characterized by a somewhat modified form of ray tissue. The 

 cells of the rays become thick -walled and sclerenchymatous. At 

 the same time the formation of ray cells upon the xylem side of the 

 cambium is retarded, so that wedges of ray sclerenchyma project 

 from the phloem into the xylem cylinder. 



Quercus rubra— The peduncle and the well nourished seedling 



stem or vigorous yearling twig 



orrnal 



