630 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VoL. VI. 
better reasons for regarding the Ranunculacee throughout as astelic, in 
Van Tieghem’s sense, than as entirely medullated monostelic, according 
to Strasburger, or in part medullated monostelic, and in part astelic, 
according to Van Tieghem. 
If the central cylinder of the Ranunculacez be throughout collateral 
siphonostelic in the sense described by the writer, it would seem 
necessary to extend that conception of the morphology of the central 
cylinder to the rest of the dicotyledonous Angiosperms. It appears 
highly probable that an exhaustive study of seedlings and floral axes of 
representatives of the various orders will result in the discovery of a 
number of facts favorable to this view, and an investigation in this 
direction is in progress. 
The writer's observations on Monocotyledons point to the same 
general conclusion, although here the reduction in size of the foliar 
lacune and the high development of the pericyclic mechanical tissues 
which has brought this division into special prominence in connection 
with Schwendener’s mechanical theories, make the demonstration of an 
internal phlceoterma much more difficult. The Aroids have been 
chosen to illustrate preliminarily the fundamental astely of the 
Monocotyledons.  Cadla palustris is throughout astelic in Van 
Tieghem’s sense; Symfplocarpus fetidus is obviously astelic in the 
young stem, while in the older axis it is apparently medullated 
monostelic, on account of the degeneration of the internal phlceoterma. 
We may preliminarily assume that the Aroids have throughout a 
pith derived from the fundamental tissues. This conclusion may be 
extended to the other Monocotyledons and it may be further stated 
that the primitive stelar condition in the Monocotyledons is tubular, 
and that the central cylinder is interrupted by foliar lacunz correspond- 
ing to the leaf-traces. The peculiar cauline course of the bundles in the 
Monocotyledons is not primitive, since it does not appear in the young 
stem. 
Taking into consideration all the facts derived from a study of the 
Angiosperms, the general statement may be made that the primitive 
type of stelar system in the group is a hollow fibro-vascular tube with 
gaps corresponding to the leaf-traces. This type of stele may appropri- 
ately be called siphonostelic. In siphonostelic axes the stelar tube may 
have both internal and external phloém, and this case may conveniently 
be described as amphiphloic. Where the internal phloém is absent, as 
is the case in the majority of the Angiosperms, the stelar tube is ecto- 
phloic. The pith is always to be regarded as merely an included portion 
of the fundamental tissues. 
ee 
