604 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vot. VI. 
Do they throw any additional light on the difficult problems of the 
genetic relationships of the group? Anatomical studies have hitherto 
been almost entirely neglected by American botanists on account of the 
wealth of other matters, and that fact will serve as a sufficient justifica- 
tion for the present research. Were any other needed, it would be 
afforded by the extremely important phylogenetic results obtained in 
recent years by English, French, and German paleobotanists from the 
study of the fossilized remains of the chiefly vegetative organs of various 
groups of extinct Cryptogams. The advance of the science of Ecology 
has furthermore made it less difficult to distinguish between those ceno- 
genetic features of structure which are the result of the adaptation of 
plants to their modern environment and those palingenetic traits which 
serve as an indispensable guide in the interpretation of phylogeny. 
as POLY S PELIGCAWPE. 
In his essay on Polystely to which reference has already been made, 
Van Tieghem‘* describes this modification of the central cylinder as origi- 
nating from the pithless monostelic type, by the successive bifurcations 
of the primitively simple stele. He has referred to it more recently in 
practically identical terms.” 
In studying morphological problems, it is an accepted method of pro- 
cedure to pass from the lower forms to the higher. This course has 
been profitably pursued in the investigation of the morphology of 
sporangia, anthers, ovules, etc.,and in the examination of the homologies 
of the gametophyte in the various groups of vascular plants. Curiously 
enough, Van Tieghem has given very little attention to the lower forms 
in his studies on the central cylinder, and still less to their development. 
In his essay on Polystely he does not describe the development of any 
cryptogamous stems of the polystelic type. It is only subsequently in 
his Traité de Botanique (p. 765), that he makes a slight reference to the 
development of the polystelic central cylinder of Pterzs aguzlina. Leclerc 
du Sablon" has given an admirable description of the earlier stages in the 
development of the stem of this species, but has apparently, not correctly 
observed the later phases. 
The writer proposes to describe briefly his own observations on this 
form, as a preliminary to the examination of the phenomenon of 
g. Op. Cit., p. 282. 
to. Traité de Botanique, 1892, p. 13703 Elements de Botanique, 1898, p. 179. 
11. Ann. Sci. Nat. Bot., 7 sér., rr Tom., Récherches sur la Tige des Fougéres. 
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