Notes. 
599 
In other genera either velum or both this and ligule have either 
quite aborted or never been developed, which is probably result of 
efficient protection of sporangia by peltate ends of sporophylls, as in 
Lepidodendron and Spencerites. 
In Equisetaceae peltate sporophylls afford necessary protection. 
W. C. WORSDELL. 
Kew. 
THE NATURE OF THE VASCULAR SYSTEM OF THE 
STEM IN CERTAIN DICOTYLEDONOUS ORDERS 1 . — The 
object of the present thesis is to show, from anatomical data, that no 
hard-and-fast line exists between the two classes of Dicotyledons and 
Monocotyledons. The hollow vascular cylinder of the stem of a great 
number of dicotyledonous orders, if not of all, has been derived from 
a system of scattered bundles such as is characteristic of the stem of 
almost all Monocotyledons. The flowering-stem and peduncle, as 
being those parts of the caulome which have undergone least modifica- 
tion owing to the necessities of adaptation to external conditions, ex- 
hibit, as a rule, most clearly the primitive structure which in the vege- 
tative parts has become obscured. The axial organs of the seedling, 
owing to their limited diameter and the small number of leaf- 
traces concerned in the building-up of the vascular system, cannot 
as a rule possibly exhibit the primitive scattered arrangement of 
the bundles. 
As the stem increased- in height and became more woody, and the 
leaves smaller and more numerous, the scattered arrangement of bundles 
in the stem (chiefly a result of the latter being mainly built up of large 
leaf-bases from which great numbers of pluriseriate bundles entered 
the axis) gradually became modified into that of a hollow cylinder, 
which was necessary both to support the bending-strains from a tall 
stem, and to facilitate the continuous centrifugal addition of new con- 
ducting-tissues by means of a secondary meristem. The stems of 
plants possessing scattered bundles support bending-strains by means 
of a sub-peripheral sclerotic band, and, in those cases where a secondary 
meristem is present, increase their conducting-tissue by the continuous 
centrifugal formation of new scattered bundles accompanied by inter- 
fascicular tissue. 
1 Abstract of paper read before Section K of the British Association, Belfast, 
1902. 
