in the Genus Primula. 3 1 1 
In these several cases, it is certain that the absence of the 
internal bundles and the consequent production of imperfect 
steles has nothing whatever to do with the production of the 
monostelic terminal floral peduncle : for plants have been 
examined which possess the imperfect type of stele throughout 
a given year’s growth, itself terminating in a floral peduncle, 
and also exhibiting the same structure again in the next 
year’s growth immediately above the peduncle. 
Among the dialystelic species I examined P. Auricula and 
P. Palinuri , and as regards their mature structure they agree 
in every respect with Van Tieghem’s description. The steles 
are perfect throughout, although a slight trace of the phe- 
nomena described in connexion with the entrance of the 
leaf-trace in P. involucrata may sometimes be discerned ; but 
only in relation to the median one of the many traces which 
enter from the leaf. 
Structure of the Petiole. 
In all the species that I examined, the vascular strands 
which pass off from the stem into the leaves are rather large 
in size, and take the form of arcs of greater or less curvature. 
In these plants at any rate, I have obtained a striking con- 
firmation of the opinion so strongly advanced by Strasburger, 
that the leaf-traces take with them, from the stele of the 
stem, not only portions of the endodermis and pericycle, but 
also of the pith and sometimes of the primary medullary 
rays 1 . This fact is particularly well shown in P. involucrata 
and P. obtusifolia . The term ‘ meristele,’ therefore, as applied 
to these vascular strands, is especially appropriate, since they 
really include portions of each of the constituent parts of the 
steles from which they arise. The leaf-trace usually takes 
away several vascular bundles from the stem-stele, although 
they are not always to be separately distinguished in the 
meristele itself. The endodermis of the meristele, whenever 
it is clearly defined, is most certainly continuous throughout 
1 Histol. Beit., Vol. iii, p. no. 
