166 BOTANICAL GAZETTE [MARCH 
as growth of the stems continues, until a good-sized, homogeneous, 
parenchymatous ray is formed. In the wood of the mature plant the 
large ray is formed more abruptly, and is not so much the result 
of fusion of smaller rays, as of the transformation of all tissue, within 
a region of the size of the ray to be formed, into ray parenchyma, such 
change being rather abrupt and occurring largely at the beginning 
of a season’s growth. The seedlings of the white oaks possess in 
their early wood only uniseriate rays, suggesting a somewhat more 
primitive state. A few living oaks show the transitional stage, that 
is, large rays composed of ununited aggregations of small rays in the 
wood of mature plants. The Japanese oaks especially belong in this 
group. 
The oaks present an excellent case of recapitulation of ancestral 
characters by seedlings. The phylogenetic history of ray structure 
in the genus is well displayed, step by step, in the wood of the seedling 
stem during the first few years. 
The work has been carried on in the Phanerogamic Laboratories 
of Harvard University. The writer desires to express his thanks 
to Dr. F..H. Knowtton of the United States Geological Survey 
for the loan of material of miocene oaks, and to Mr. I. W. BAILEY 
for opportunity to examine and use slides of several genera of cupu- 
liferous woods. He is also very much indebted to Professor E. C. 
JErrRey for suggestions and advice during the progress of the investi- 
gation. 
HARVARD UNIVERSITY 
EXPLANATION OF PLATES VIII AND IX 
PLATE VIII 
Fic. 1.—Quercus rubra; transverse section of wood, showing noistent: of 
large and small medullary rays. X40 
Fic. 2.—The same; tangential rect of wood, showing similar rays. X49. 
Fic. 3.—Quercus velutina, seedling; transverse section of portion of stem 
showing formation of large rays. X40. 
Fic. 4.—Quercus rubra, seedling; tangential section of a large ray in process 
of formation. X4o. . ys 
Fic. 5.—Fossil oak from gold gravels of California (Miocene); transverse 
.section of wood showing portion of the large ray. 40 
Fic. 6.—The same; tangential view of portion of the cag ray. X40: 
