I910] BAILEY—TRAUMATIC OAK WOODS 375 
structures; and has demonstrated the presence of traumatic mar- 
ginal tracheids in the wounded wood of Cunninghamia sinensis.® — 
An interesting parallel to the work of JEFFREY upon traumatic 
reversions in the Coniferales has been noted by the writer in the 
traumatic reversions of wounded oak wood. Owing to the con- 
troversy which exists as to the relative primitiveness of the Abietin- 
eae and Cupressineae this occurrence of traumatic reversions in 
a dicotyledonous genus is of particular interest in demonstrating 
the application of the principles of experimental morphology to 
plants. 
Before describing the reversionary characters of oaks, it will 
be well to have clearly in mind the normal structure of the wood 
of existing oaks, and also that of ancestral types. As is well 
known, the secondary xylem of living oaks consists of vessels, 
fibers, tracheids, and parenchyma. The last occurs vertically 
as wood parenchyma, and horizontally disposed in plates of tissue 
extending radially, the so-called primary and secondary medullary 
rays. The ‘“‘primary rays’’ (fig. 1) are the distinctive feature of 
oak wood, the “silver grain,” and are broad, fusiform masses, 
many cells in width, which are supposed to originate as inclusions 
of fundamental tissue between the primary fibrovascular bundles. 
The “secondary rays” are thin sheets of tissue, and consist of a 
single row of cells when seen in tangential or transverse section 
(fig. 1). These rays, unlike the primary rays, are supposed to 
originate only with secondary growth. 
In contrast to this type of structure occurring in the mature 
Wood of extant oaks, Eames has shown’ that certain miocene 
oaks do not possess large rays composed of homogeneous masses 
of ray parenchyma, but have in their place bands of aggregated 
smaller rays which are separated by fibers and wood parenchyma. 
These rays are homologous with the “false rays” of the Betulaceae, 
and lead to the conclusion that the so-called primary rays of extant 
oaks have been built up by an aggregation and fusion of numerous 
originally uniseriate rays. 
“— epee! tracheids in Cunninghamia sinensis. Annals of Botany 22: 593- 
70On the chica of the broad ray in Quercus. Bot. GAZETTE 49:161-166. pls. 
89, Igio, 
