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. 



IN 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 : 



i. Oaks from the Miocene 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.] 



