The Relation of the Leaf-trace to the Formation 
of Compound Rays in the Lower Dicotyledons . 1 
BY 
IRVING W. BAILEY, A.B., M.F. 
Instructor in Forestry and Wood Technology at Harvard University. 
With Plates XV-XVII and one Figure in the Text. 
T HERE exists in the wood of dicotyledonous plants considerable varia- 
tion in the size, shape, and structure of the radially disposed plates of 
parenchyma, commonly designated medullary rays. This diversity of 
structure is well illustrated by several well-known genera of the Cupuliferae. 
Alnus and Castanea , for example, are characterized by possessing numerous 
small linear or uniseriate rays, rays similar in form and structure to the 
small rays which are a distinctive feature of the wood of coniferous plants. 
Occurring with this type of ray, and in marked contrast to it, are the large 
fusiform masses of parenchymatous tissue, often called primary rays, which 
occur in Quercus. Fagus , like the oak, possesses both the small linear or 
uniseriate and the large multiseriate type of ray, and in addition smaller 
multiseriate rays which are graded in size between these two extreme 
types. Betala , Carpinus , Ostrya , and Corylus possess usually, in the mature 
wood, numerous bi- and tri-seriate rays, among which are to be found 
scattering rays of the linear type. Finally in the lower Cupuliferae, Alnus, 
Betula , Carpinus , and Corylus, bands or aggregations of uniserate rays occur, 
and have been described by certain writers as ‘ false rays 
The occurrence of ‘ false rays ’ in sections of a fossil oak from the gold 
gravels of California (Miocene) led Mr. A. J. Eames of this laboratory to 
investigate seedling and fossil oaks for evidence which might demonstrate 
what relation, if any, existed between the large multiseriate rays of living 
oaks and this 1 false ray’ of the Miocene oak. At the same time the writer 
carried on a series of investigations upon the distribution and origin of the 
‘false’ and the large multiseriate rays in the Cupuliferae and other 
1 Contributions from the Phanerogamic Laboratories of Harvard University, No. 27. 
[Annals of Botany, Vol. XXV. No. XCVIX. January, 1911.] 
Q 
