The Evolutionary History of the Foliar Ray in the 
Wood of the Dicotyledons : and its Phylogenetic 
Significance . 1 
' BY 
IRVING W. BAILEY, A.B., M.F. 
Assistant Professor of Forestry at Harvard University. 
With Plates LXII and LXIII. 
Evolution of the Foliar Ray. 
I N 1909 Mr. Eames (4) and the writer (1, 2, and 3) conducted a series 
of investigations upon the broad rays and so-called ‘ false rays ’ of the 
Fagales. The conclusions drawn from these studies have since been 
published, and may be summarized briefly as follows : 
1. Oaks from the l\Jiocene of California are characterized by possessing 
‘ false rays such as are a distinctive feature of the wood of a large number 
of living representatives of the Betulaceae. 
2. The mature wood of certain Live Oaks of America and Japan possess 
large rays which are composed of congeries of smaller rays. 
3. Alnus rhombifolia , Nutt., and A. maritima , Muehl, develop in the 
older wood large homogeneous sheets of ray parenchyma homologous to the 
large rays of oaks with deciduous foliage. 
4. The earliest formed secondary wood of seedling oaks and alders 
possesses solely uniseriate rays, such as are a characteristic feature of coni- 
ferous plants and many other Gymnosperms. 
5. In the mature wood of different species of Alnus a perfect series of 
stages occur, which demonstrate the ‘ building up * of a homogeneous sheet 
of ray parenchyma from congeries of uniseriate rays and the parenchymatiza- 
tion of fibres included between them. 
6. In the development of individual alders and oaks a similar pro- 
gressive series of compounding stages occur in passing from the younger to 
the older portion of the stem. 
7. Wood which possesses highly developed types of compound ray 
tissue when injured severely reverts to the primitive uniseriate condition, 
1 Contributions from the Phanerogamic Laboratories of Harvard University, No. 47. 
[Annals of Botany, Vol. XXVI. No. CIII. July, 1912.] 
