628 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vou. VI 
always a continuous hollow cylinder of fibro-vascular tissue, bounded 
internally and externally by phlceotermal sheaths, which communicate 
through the foliar lacune, and is in fact primitively of the conformation 
described by Van Tieghem as gamodesmic or gamomeristelic. The use 
of these terms, however, seems inappropriate, since they imply the union 
of bundles or meristeles originally separate. The writer has suggested 
the term siphonostelic as fitly describing the stelar type occurring in the 
stem of Preris aqguilina or Primula farinosa. The question may now be 
asked whether this term should not also beapplied to the very similar stelar 
conformation found in the Ranunculacee and Nymphzaceze. The most 
striking difference between the stelar systems of the two types is the 
absence of an internal phloém in the case of the Nymphzacez and 
Ranunculacee. But Gwynne-Vaughan has called attention to the fact 
that the collateral fibro-vascular strands of the Nymphzacez often 
become concentric, an observation which the present writer has been 
able to confirm. On the other hand, the siphonostelic central cylinder 
of Primula zaponica and P. farinosa starts as a collateral stelar tube, 
only subsequently becoming more or less completely concentric. In the. 
floral axes of these species, moreover, both the internal phloém and the 
internal phlceoterma disappear, giving rise to a central cylinder, which, 
if its mode of origin had not been followed, would be regarded as 
medullated monostelic. The flowering stems of all the described species 
of so-called polystelic Primulas have the same peculiarity, It has been 
shown in the earlier part of this essay that the stelar strands of Parnassza 
palustris, within an interval of a fraction of a millimetre, may be 
successively collateral and concentric, while in P. parviflora the cauline 
strands are collateral and the leaf-traces concentric. The two types of fibro- 
vascular strand pass imperceptibly into each other in the Angiosperms, 
and, as will be subsequently shown, also in the Gymnosperms and the 
Vascular Cryptogams. It would appear from the study of development 
that Van Tieghem’s polystelic and astelic types are essentially the same, 
inasmuch as the stelar system in both cases is primitively a tube with — 
foliar lacune. Further, the presence or absence of internal phloém 
appears to be a matter of slight morphological importance. 
III—We may now pass to the question of the morphology of the 
medullated fibro-vascular axis, bounded by an external phlceoterma 
only. It has already been pointed out that Van Tieghem regards the 
central cylinder in this type as derived from the pithless stele of the 
hypocotyl, by dilatation and the formation of a parenchymatous medulla, 
differing morphologically from the fundamental parenchyma outside the 
stele. It has also been mentioned that Van Tieghem considers that his 
medullated monostelic type of central cylinder, and his astelic type, may 
