612 TRANSACTIONS OF THE CANADIAN INSTITUTE, [VoL. VI. 
If a transverse section of the internodal region of Parnassia palustris 
be microscopically examined, it will be discovered that the stele is 
provided with a pith formed of thick-walled collenchymatoid cells. 
There is considerable secondary growth present in the woody zone 
traversed by slender medullaryrays. The central cylinder issurrounded by 
a well-marked and lignified endodermis, which appears very clearly after 
the use of phloroglucin and hydrochloric acid. Most of these features 
may be seen in photograph 25, plate 11. In a section passing through 
the point of origin of a leaf-trace, the side of a central cylinder is seen to 
be hollowed opposite the outgoing trace ; at the bottom of the concavity _ 
the phloém and xylem are absent, so that the collenchymatoid tissue of 
the central cylinder of the stele is only separated from-the external 
fundamental tissue by the pericycle and endodermis. Not unfrequently 
two leaf-traces come off from the stele, nearly opposite each other, as 
may be noted in photograph 26, plate 11. When this happens the 
central cylinder is split for a short distance into two strands. At their 
lowest point the two strands are devoid of internal phloém and xylem, and 
have along their inner borders a layer of the pith-like tissues described 
above. The latter is separated from the fundamental tissue passing 
through the stele of this region, only by the pericycle and endodermis. 
These features may be seen in photograph 27, plate 11. Higher up, the 
fibro- vascular tissues cover over the internal faces of the two strands 
again, and they become, to employ Van Tieghem’s terminology, two 
separate steles, each of which apparently possesses a medulla of its own. 
Photograph 26, plate 11, sufficiently illustrates the description given 
above. The photograph very closely resembles Fig. 33, plate 15 of 
Gunnera magellanica in Van Tieghem’s memoir on Polystely. 
The points of interest in the anatomy of this species seem to be that 
there is present an apparently medullated monostelic axis, which 
continues as such unless two leaf-traces from it come off close together ; 
that under these circumstances the divided stelar axis becomes at first, 
astelic, and then a little higher up, polystelic, in Van Tieghem’s sense of 
these terms. It is further to be noticed that both astely and polystely 
are closely related to the exit of leaf-traces. 
In Parnassta parviflora the central cylinder is astelic, or rather gamo- 
desmic, since it consists of a collateral fibro-vascular tube with an internal 
endodermis, which communicates with that outside, through the gaps 
occurring in the cylinder opposite the points of exit of the leaf-traces. 
A section of the central cylinder of this species is shown in photograph 
29, plate 11: Zis an outgoing leaf-trace ; g? is its corresponding gap, 
and g! is that of an earlier trace; ~ andr? are strands belonging to roots, 
