THE RAY SYSTEM OF QUERCUS ALBA 
LADEMA M. LANGDON 
(WITH TWENTY-TWO FIGURES) 
Introduction 
The medullary rays of Quercus alba are of three distinct types: 
uniseriate rays, thin, linear sheets of tissue of a single layer of cells; 
multiseriate rays, two or more cells in width and many cells in 
height; and compound rays, which are broader than either of the 
first two mentioned and consist of extensive homogeneous masses 
of parenchyma. Between the uniseriate and the compound types 
there exist numerous transitional stages, representing either dis- 
integration of the broad ray into a number of narrow ones or the 
integration of many uniseriate rays to form the compound rays. 
Figs. 9 and 10 illustrate these three principal types. 
The evolution of these different types of rays and the relation- 
ships between them have recently been the cause of much discus- 
sion and the subject of a series of investigations carried on chiefly 
in the laboratories of Harvard University. This particular line 
of investigation was initiated in 1909 by JEFFREY (7) when he 
proposed the “aggregate ray hypothesis.’””’ He maintains that 
paleobotanical evidence points to the probable derivation of the 
existing oaks from ancestors which possessed only the linear type 
of ray, and that the broad rays so characteristic of the present oak 
wood have been formed by a gradual aggregation of uniseriate rays. 
His arguments favoring the “aggregate ray hypothesis” have 
since been perfected and worked out in greater detail by Eames 
(5, 6) and by Batzey (1, 2,3). Eames (5) has demonstrated from 
a study of fossil and seedling oaks that the broad type of ray has 
originated by the aggregation or fusion of many of the small 
uniseriate rays through the transformation of the included fibers 
and wood parenchyma into ray parenchyma. He agrees with 
JEFFREY (7) that in the fossil oaks and in the seedlings of modern 
oaks only the linear type of ray isfound. Battery (2) has developed 
313] (Botanical Gazette, vol. 65 
