318 BOTANICAL GAZETTE [APRIL 
rays, but by a sudden checking of the development of all tracheidal 
tissue within the immediate vicinity of the ray and the consequent 
continued growth of parenchyma in this region. This abrupt 
change usually occurs at the beginning of a year’s growth. Figs. 9 
and 10 show t sections of portions of such rays at the points 
where they abruptly broaden, and illustrate very clearly the manner 
in which this type of ray originates. These three types of com- 
pound rays occur generally in all sections of the mature wood, but 
the wedge-shaped, gradually tapering ray, as seen in transverse 
section, appears to be the characteristic type of broad ray in this 
species of oak. 
A very peculiar and constant feature of the multiseriate and 
compound rays is the manner in which they are broken up, upon 
entering the cortical region of the stem, into wedge-shaped masses 
of ray parenchyma. No such interruption or breaking up of the 
thin, linear uniseriate rays is apparent. 
A careful study of different sections from the lower, central, 
and top regions of the same tree (figs. 11, 12, 13) makes it evident 
that the region of the tree from which the wood comes is only a 
slight factor, if any, in the modification of the ray system. On the 
other hand, a comparison of all sections of shoots of the same age 
from the three trees reveals a marked diminution in the diameters 
of stems from trees II and III, but this may be due chiefly to the 
effects of retardation in growth of these two trees rather than to a 
difference in age. 
EFFECT OF SUPPRESSED GROWTH ON RAY SYSTEM.—The retarding 
effect of suppressed growth on the medullary ray development is 
easily seen in figs. 17, 18, and to. Although wide rays occur in 
these suppressed twigs, they are neither so wide nor so deep as in 
the case of the vigorous shoots. Especially in some of the older 
stems from tree III the development of wide rays has been retarded 
to such an extent that only uniseriate rays occur, even in mature ~ 
rr and 12 year old wood (fig. 22); and in numerous specimens of 
wood 15~19 years old, taken from different regions of this same tree, 
wide rays are entirely absent up to about the tenth or eleventh 
year, when broad rays often appear abruptly, the phase of com- 
pounding being confined to one or two annual rings (fig. 16)- 
