322 BOTANICAL GAZETTE [APRIL 
depression of the secondary xylem in the concave segments is the 
proportionate increase in amount of phloem above these segments. 
With two exceptions, all of the seedlings used in this investi- . 
gation were germinated and grown under greenhouse conditions, 
averaging 1.75-3 inches in height. Here, as in the case of the first 
annual ring, uniseriate rays are the prevailing type, multiseriate 
rays 3 and 4 cells in width appearing only in the vicinity of lateral 
leaf traces. 
Summary 
t. It was chiefly with the purpose of determining the effect 
of certain conditions upon the ray system of Quercus alba, such as 
the age of the trees, location of shoots in the trees, and vigorous 
or suppressed conditions of growth, that this investigation was 
undertaken. 
2. The results obtained indicate that neither the age of the 
trees nor the location of wood in a tree is an appreciable factor in 
the modification of the ray system. 
3. The conditions of vigorous and suppressed growth, however, 
are problems to be considered. With decreasing vigor of growth 
in the mature wood multiseriate rays appear at chicas later 
stages in the development of the stem. 
4. Multiseriate rays, 2-6 cells in width, occur in the seedlings 
and the first annual ring of Quercus alba only in the vicinity of 
lateral leaf traces. 
5. The peculiar formation of the cambium and wood in the 
stem of the oak, whereby 5 wedge-shaped segments of secondary 
xylem are formed, including between them 5 narrow depressed 
segments, is due directly to the influence of the outgoing leaf traces 
upon the general growth and form of the woody cylinder. 
This investigation was undertaken at the Botanical Laboratory 
of Oberlin College, and the sincerest thanks of the writer are due 
to Professor FREDERICK O. Grover and to Dr. SusAN P. NICHOLS 
for their kind assistance. Grateful acknowledgment is also made 
of the valuable criticism and advice given by Dr. CHARLES J. 
CHAMBERLAIN and Dr. W. J. G. Lanp during the continuation — 
of the work at the University of Chicago. 
UNIVERSITY OF CHICAGO 
