ioo6 
Thompson .— On the Origin of the 
the storage of the food manufactured in the leaf is, of course, in the stem 
adjacent to the leaf-trace. Accordingly the storage organs, i. e., the rays, 
at this point in the stem have been enormously developed, especially in 
view of the probable persistent habit of the leaves of Angiosperms during 
the warmer Mesozoic times. Then, following its development at the leaf- 
trace, the broad ray has spread throughout the plant. Bailey has also 
suggested that the further development of compound rays at the expense 
of the woody cylinder has given rise to the herbaceous habit among 
Angiosperms. The same conclusion was reached by Eames 1 after an 
investigation of herbaceous and semi-herbaceous forms. This aspect of the 
work has resulted in a conclusion exactly the reverse of the commonly 
taught Sachsian hypothesis of the development of the woody cylinder from 
the herbaceous type by the filling in of the interfascicular regions through 
the activity of the so-called interfascicular cambium. 
It will be observed that the only kind of ray not included in these 
investigations is the multiseriate type, that intermediate in size between 
the uniseriate and compound types. It is the object of this paper to 
determine the origin of this ray and to establish its position in the general 
scheme of ray development in the Dicotyledons. In carrying on the 
investigation it was found that the Ericaceae presented very favourable 
conditions, and this family was studied in detail. Confirmatory evidence 
was found in many other groups. 
The origin of the multiseriate ray is epitomized in PI. LXXVII, Fig. i. 
This is a photograph of a transverse section of Rhododendron pjmctatum 
(Andr.) just above the level of exit of the leaf-trace. All the rays in the 
section are seen to be uniseriate except the conspicuous group at the top, 
which is directly above the leaf-trace. At this point we see next to the pith 
a broad compound ray which during its course through the wood breaks up 
progressively into several smaller multiseriate rays. Otherwise stated, the 
group of multiseriate rays has originated by the breaking up of a com¬ 
pound ray. 
A tangential view of this group of rays is presented in Fig. 2. At the 
bottom of the field is the leaf-trace, and extending upward from it com¬ 
pletely through the field and for a long distance beyond is the aggregation 
of multiseriate rays. A small group also extends for a very short distance 
below the trace. Complete series of such tangential sections through the 
node from* the bark to the pith show that all the multiseriate rays in the 
branch are associated in this manner with the traces. Complete series of 
transverse sections through the node show that the solid type of broad ray 
is not present at the pith through the whole vertical extent of the group, 
but at the upper extremity multiseriate rays arise directly from the pith. 
1 Eames, A. J.: The Origin of the Herbaceous Type in Angiosperms. Ann. Bot., Jan. 1911, 
pp. 215-224. 
