238 Worsdell . — The Vascular S true here of 
As a general theory resulting from the preceding investi- 
gations, it appears to me a quite probable view that the 
sporophyll in Cycadaceae is a more primitive foliar organ 
than the foliage-leaf, and for the following reasons : — 
a. The theory of Bower with regard to the development 
and morphology of spore-producing members in the Lyco- 
podineous series of plant-forms and the phylogenetically late 
appearance of assimilating foliar appendages, which arise by 
progressive sterilization of the tissues of the former, appears 
to me to be a highly natural hypothesis and one containing 
a large element of truth. 
Now, it seems to me highly probable that the Fern- 
sporophyte had a very similar origin, that it also arose from 
a fertilized oospore which, instead of producing motile re- 
productive organs, gradually replaced these latter by asexual, 
non-motile spores contained in sporangia which eventually 
became raised into an aerial position by progressive steriliza- 
tion of the tissues of the young developing sporophyte : 
a theory which will not be accepted by those who incline 
to the view that the Fern-sporophyte had an entirely different 
origin from that of the Bryophytes 1 , with which group it is 
here my purpose to emphasize its similarity of origin. There 
is, in fact, no reason to think that the order of development of 
the two kinds of foliar appendages, sporophyll and foliage- 
leaf, should, in the Fern-series, have been fundamentally 
different from that in the Lycopodineous series : the onto- 
genetic developmental history of the two types is to-day so 
similar as to point to the probability of their phylogenetic 
developmental history having been also similar. 
This being so, we may assume that evolution may have 
proceeded as follows. First in order of time, sporophytes 
which bore sporophylls only would exist ; next to these 
would succeed those in which both sporophylls and assimi- 
lating foliar organs were present. But it is quite conceivable 
that subsequent modification of all the sporophylls might 
1 Scott, Address to Botanical Section of Brit. Assoc. Meeting, Liverpool, 1896, 
pp. 9-10. 
