573 
Bower.—On Medullation in the Pteridophyta . 
of the parts of the shoot. The consequences of this are reflected struc¬ 
turally even down to the pith itself, which, according to the habit and pro¬ 
portions of the shoot in question, may arise from more deeply seated, or 
successively from more superficial sources. That is the result which emerges 
from this study of medullation in the Pteridophyta. 
The medullation of the Seed Plants, and ultimately of the Higher 
Flowering Plants, has not been touched upon here. But it is plain that any 
broad conclusion as to the origin of the pith in the Pteridophyta must 
affect the theoretical position as regards them. And those who hold that 
in the Pteridophyta the pith may be either intrastelar in origin or extra- 
stelar will be prepared to extend such views to the Seed-bearing Plants. 
It has, however, been pointed out above that the establishment of the 
phyletic history of the pith in any one line of descent cannot have any 
direct bearing upon that of any other, unless it can be proved that the 
origin of the pith antedated the phyletic segregation of the stocks in 
question from a common ancestry. Applying this in the case of Seed 
Plants, the fact of solenostelic structure in such a Fern as Pteris aqnilina 
can have no direct bearing upon questions of their medullation, unless it 
can be shown that the Pterideae had a common ancestry with the Seed 
Plants compared, and that that ancestry was already medullated and soleno¬ 
stelic before the two phyla were segregated. The present drift of investiga¬ 
tion indicates that it is not in the direction of any solenostelic type of 
Ferns, as we now know them, that we shall look for the phyletic origin of 
any Seed Plants. It would be more to the point to inquire how the 
medullation was initiated in the Pteridosperms and other primitive Seed 
Plants, for their structure would throw a more direct light on the question. 
Moreover, what is required as a foundation for an opinion on the medulla¬ 
tion of Seed Plants would be not merely the observation of isolated sections, 
but, so far as the material permits, a comparison of stems of different ages, 
in Lyginodendron for example, and of allied plants from different geological 
horizons. A knowledge of the origin of their pith arrived at in this way 
would provide a necessary test of the theoretical position of Professor 
Jeffrey on the stelar morphology of the Higher Flowering Plants . 1 
Finally, it must be said again that there is no wish to prejudge the 
question whether the endodermis is or is not an immutable barrier between 
the external and internal systems of tissue. Certain examples of irregular, 
and even of sporadic development of endodermal characters in tissues apart 
from the usual positions for endodermis, would seem to indicate that endo¬ 
dermal structure may sometimes originate de novo. The whole discussion 
has proceeded on the understanding that this question is left open for 
future demonstration. FI ere the endodermis itself has served as a con- 
1 Jeffrey, The Morphology of the Central Cylinder in the Angiosperms. Reprinted from the 
Trans. Can. Inst., 1900. 
Qq 
