632 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VoL. VI. 
manifest some features of phylogenetic importance. The writer has 
pointed out that siphonostely exists under two modifications among the 
vascular Cryptograms, vzz., siphonostely, in which the gaps of the stele 
correspond to leaf-traces; and siphonostely, in which there are no foliar 
gaps, but in which the stelar lacune correspond to branches. He has 
designated the former type phyllosiphonic; the latter, cladosiphonic. 
The use of this distinction, together with all other available character- 
istics, results in the placing of the Lycopodiales and Equisetales near 
one another in the system as groups which are invariably cladosiphonic. 
The Filicales,s Gymnosperme, and Angiosperme, on the other hand, 
are uniformly phyllosiphonic. The writer does not intend to go further 
into this matter in the present memoir, but it may nevertheless be sug- 
gested that there are two distinct primitive groups of vascular plants, 
vig., the Lycopsida and the Pteropsida. To the former group belong 
the Lycopodiales and Equisetales ; to the latter, the Filicales, the 
Gymnosperme, and Angiosperme. The validity of the classification 
indicated above, in the case of Lycopsida, has already been discussed by 
the writer,! in his memoir on the genus Equisetum. The considera- 
tions which favor the setting up of the other great alliance can be 
more advantageously examined subsequently. 
V. If the writer has correctly interpreted the anatomical facts 
described and figured in the present memoir, the morphological ideas 
of Van Tieghem can no longer be accepted in full. It is the great 
merit of that distinguished botanist to have recognized in so large a 
measure the essential unity of the fibro-vascular system of plant axes. 
That he should have gone too far in the direction of unity in the case of 
the so-called medullated monostelic type, and not far enough in 
his polystelic type, is to be explained by the comparatively slight 
attention given by him to the subject of development. Strasburger, 
in respect to monostely, has gone even further than Van Tieghem, 
for he unites Van Tieghem’s astelic type with the medullated 
monostelic, and regards the medulla in both cases as_ intrastelar 
parenchyma. An examination of the anatomy of the young axis 
apparently brings us back to the standpoint of De Bary in regard 
to the morphology of fibro-vascular strands. The older anatomist, 
however, on account of his intentional neglect of ontogeny, appears 
to have completely overlooked the morphological unity of the cauline 
fibro-vascular apparatus of the Angiosperms. 
Since it is impossible to investigate experimentally any but the 
54. Mem. Boston. Soc. Nat. Hist., Vol. 5, No. 5. 
