649 
Foliar Ray in the Wood of the Dicotyledons. 
Fig. 15 the ten sheets of ray tissue are distributed in five pairs of approxi- 
mated rays. This approximation of the lateral leaf-trace rays enables 
their concentrated retarding influence upon growth to depress the included 
segment of tracheal tissue below the general contour of the stem (PI. LXII, 
Fig. 3, and PI. LXIII, Figs. 13, 15). In addition to the lateral leaf-trace rays* 
foliar rays are developed in oak and other plants in relation to the median 
traces of the leaf. However, in oak these rays are in most cases less strongly 
developed in the young twig than are the rays related to the lateral traces. 
6. The origin and development of foliar rays show clearly that the 
statements of Sanio, Sachs, and de Bary, pointing to the origin of large 
rays as inclusions of fundamental tissue or ground parenchyma between 
putative fibro-vascular bundles and the development of so-called fascicular 
and interfascicular segments from supposed fascicular and interfascicular 
cambiums, lead to extremely misleading conclusions. 
7. All segments of the stem are essentially ‘fascicular’, since in the 
seedling plant of primitive Dicotyledons the stele is an undivided tubular 
cylinder without indication of the putative fascicular and interfascicular 
segments and large rays. 
8. The development, in relation to the traces of the leaves, of large 
sheets of storage tissue from congeries of uniseriate rays has a strong 
dissecting effect upon the stele, producing the supposed fascicular and inter- 
fascicular segments of oak, vines, and semi-herbaceous plants. 
Eames (5), in an investigation of herbaceous and semi-herbaceous Angio- 
sperms, secured interesting evidence which indicates strongly that herbaceous 
Angiosperms have been derived from forms which possessed strongly 
developed secondary growth. In the life-history of many plants there 
occurs a transition from a tubular stele, in younger portions of the plant, 
to a ring of separate fibro-vascular bundles in subsequently formed parts 
of the stem. For example, the prostrate biennial or perennial stems of 
Potentilla palustris , Scop., as well as the seedling plant, possess an unbroken 
central cylinder, whereas the cylinder of the erect annual stem a short dis- 
tance above the rhizome breaks down into a typically herbaceous ring of 
separate bundles. The herbaceous type of central cylinder has resulted, 
therefore, from the reduction in size of Dicotyledonous plants in later 
geological periods, coupled with the evolution of foliar rays whose dissecting 
effect has been progressively increased. 
More recently Professor Groom (6) has published the results of an 
investigation upon the annual ring and medullary rays of Quercus. There 
are certain fundamental objections to the conclusion reached by Professor 
Groom, that ‘ it is impossible at the present to decide whether in Quercus the 
broad-rayed or the narrow-rayed type was primitive ’. 
In studying lines of evolutionary modification in plant structures it is 
essential not only that a careful study be made of the comparative anatomy 
