652 Bailey. The Evolutionary History of the 



three sets of facts denote that in some way the pair of high rays, together 

 with the tissue between them, is equivalent to a single broad ray ; and the 

 very considerable inward dip of the annual ring between the two rays finds 

 simplest explanation in the assumption that in the ancestor the complex 

 mass represented solely ray tissue.' This conclusion is somewhat remark- 

 able in view of the facts pointed out by the writer in a former paper, that 

 the depressed segments of the oak stem are produced (see PL LXII, Fig. 3, 

 and PI. LXIII, Figs. 13 and 15) by the concentrated retarding effect upon 

 growth of two closely approximated foliar rays. Since these rays are usually 

 related to the traces of different nodes it is difficult to conceive of their origin 

 from the dissection of a single large ray. The writer recently examined 

 material of Quercus spicata, sent from India by courtesy of Mr. R. S. Pearson, 

 Imperial Forest Economist, and is unable to agree with Professor Groom 

 in stating that vessels are absent from the depressed segments included 

 between approximated pairs of foliar rays. Professor Groom for some un- 

 explained reason completely ignores the important relation of the leaf-trace 

 to the formation of large rays, although he refers to the paper by the writer 

 in which this evolutionary process was described. 



Since conducting the investigations which have been summarized 

 earlier in this paper a more comprehensive study has been made of 

 Dicotyledonous plants. This investigation has included not only numerous 

 species of the more primitive or supposedly primitive families, but also 

 of the higher or supposedly more recent families. The material used com- 

 prised not only species from the temperate regions of North America, 

 Europe, China, and Japan, but in addition representatives of a more tropical 

 flora from India and Australasia. In connexion with instruction upon the 

 anatomy of American woods material of practically all American trees and 

 larger shrubs has been examined. This investigation has confirmed strongly 

 the conclusions reached in regard to the origin, development, and dissecting 

 effect of foliar rays, and has served to emphasize the important part that 

 these structures have played in the evolution of modern Angiosperms. As 

 might naturally be expected in viewing this evolutionary movement from 

 a broader and clearer standpoint, certain obscure and imperfectly understood 

 features have been clarified. 



That the evolution of the foliar ray occurred in the early history 

 of Angiosperms is seen from the fact that the most convincing evidence 

 of the compounding process is confined largely to primitive Dicotyledons 

 or to regions of phylogenetic significance, and from the fact that in the 

 majority of woody Angiosperms this primitive type of foliar ray has been 

 changed structurally or completely reduced. This conclusion is further 

 emphasized by the occurrence of well-developed foliar rays in Angiosperms 

 of the upper Cretaceous (11). 



In the light of recent investigation the foliar rays appear to have 



