652 Bailey . — The Evohitionary 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 Querais 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 
