314 Gwynne- Vaughan.— On Poiystely 
the petioles of the Cucurbitaceae and Solanaceae. In the latter, 
as Strasburger points out, the tissue which Van Tieghem 
regards as pith is really only enclosed cortical tissue, and is 
not continuous with the pith of the stem at all. 
In spite of the discovery of these polystelic petioles in the 
Primulas, the fact that the Gunneras are more deeply imbued 
with the phenomenon of poiystely still holds good ; for they 
possess polystelic floral peduncles also, while those of the 
Primulas are monostelic. As regards the possession of 
polystelic petioles, I was at first under the impression that 
these two genera stood alone among the Phanerogams. But, 
from an interesting paper recently published by M. Casimir 
de Candolle \ I gather that in certain species of Alchemilla 
(A. vulgaris , &c.) the petioles contain structures precisely 
similar to those described above, and which I take to be 
steles also. This resemblance becomes the more remarkable 
on account of the fact that another feature, cited by M. de 
Candolle as characteristic of the Alchemillas, is also excel- 
lently demonstrated in certain Primulas [P. involucrata , obtusi- 
folia , and japonka ), namely, that in these plants the vascular 
system of the axillary shoot is not directly connected with 
one of the stem-steles, but with the leaf -trace itself , joining 
on to the latter some distance before it takes its place in 
the central ring of vascular tissue in the stem. 
Considering these facts as a whole, it appears that in 
P. japonica and P. denticulata a leaf-trace is capable of 
transforming itself into a stele at any point in its course 
whenever it may be advantageous to do so. Thus, if such 
a leaf-trace be followed throughout its downward course, at 
first, in the upper part of the lamina, it is found to be 
a perfectly collateral meristele. Towards the base of the 
lamina, or at any rate throughout the petiole, it exercises 
the capability which it possesses of producing internal bundles 
on its upper side, and thereby converts itself into a perfect 
stele. On arriving at the periphery of the stem it again 
1 Bull, de BHerbier Boissier, T. I, No. 10. 
