Compound Rays in the Lower Dicotyledons . 237 
species figured, which has only a slight amount of storage tissue associated 
with the leaf-trace, the foliar gaps are not persistent for any considerable 
distance above the node. In Fig. 18, on the other hand, is illustrated an alder 
in which long lines of storage tissue have been developed in relation to the 
leaf-traces. Above the node the storage tissue extends to the more or less 
persistent and elongated foliar gaps. This relation of the aggregate rays 
to the leaf-traces, which is found in the more highly specialized Cupuliferae 
with large aggregate rays, produces in the stem a segmented appearance 
of the central cylinder which has been erroneously taken to indicate the 
origin of the woody cylinder from a ring of originally separate, so-called 
primary bundles. In Figs. 19, 21, and 23 the formation of the aggregate 
ray and its relation to the enlarged foliar gap is illustrated in Aluus 
japonica by serial sections. 
From this consideration of the origin and development of aggregate 
rays, and their modifying influence upon the primitive stele of the Cupuli- 
ferae, it appears that the Sachsian theory of secondary growth must be 
exactly reversed in order to agree with the anatomical evidence afforded 
by a comparative developmental and experimental study of the lower 
Dicotyledons. Furthermore, the general examination of the anatomy of 
fossil and extant plants reveals the fact that the primitive condition of the 
fibro-vascular system was a continuous hollow cylinder. Further, in the 
evolution of modern seed plants there has been a more or less pronounced 
reduction of the amount of primary xylem of the central cylinder. This 
reduction of the primary tissues has, in most cases, progressed unevenly 
along the inner circumference of the stele, and, as a result, in many cases 
well developed areas of primary xylem are separated by areas in which 
only traces of primary elements or none at all occur. In Angiosperms the 
primitive condition of the stele is a continuous tubular cylinder. This has 
been pointed out by Jeffrey 1 in a study of the Ranunculaceae, Nymphaeaceae, 
and Saxifragaceae, by the writer, as has been shown in this article, in the 
Cupuliferae, and byEames,in an article which appears contemporaneously with 
this, in certain semi-herbaceous Rosaceae. In the development of the latest 
dicotyledonous plants, the protoxylem elements of the solid tubular cylinder 
have become gradually more or less localized, first into a primary ring with 
localized thickened areas, separated by areas from which the protoxylem 
has nearly disappeared, and finally into a dissected cylinder or ring of 
separate primary bundles. The origin and development of large sheets 
of storage tissue by the parenchymatization of certain radii of the secondary 
xylem, in connexion with the leaf, and the formation of elongated more or 
less persistent foliar gaps in relation to these structures, appear to have 
been the controlling factors in the localization of primary elements, and 
1 Jeffrey, E. C. : The Morphology of the Central Cylinder in Angiosperms. Trans. Canad. 
Inst., vol. vi, 1899. 
