132 
W. C. Worsdell. 
stages are afforded by such types as the Fern and Equisetum, in 
which the cotyledons are relegated to a more and more restricted 
area of the epibasal region. It is possible that the primitive con¬ 
dition of Ceratopteris has been retained owing to its aquatic habit; 
in view of my belief that the Monocotyledons as a class are in many 
ways so much more primitive than Dicotyledons, viz., in their 
N 
vascular anatomy, mechanical strengthening apparatus of the stem, 
construction' of flower, etc., I hold the idea of the cotyledon as 
being the result of fusion of two organs as untenable and highly 
unlikely. The facts of comparative embryological history are, in my 
opinion, as valuable evidence as any other for deciding the mor¬ 
phology of an organ ; at this early stage modifications and later 
adaptations have often not had time to assert themselves and, more 
or less clearly, the phylogenetic history is recapitulated. This 
is an instance in which phylogeny must take its clue from ontogeny, 
being the converse of what I stated above. 
This being the mode of development it follows that the 
primitive foliar organ was a fertile sporophyll and that the vege¬ 
tative leaf is a purely secondary structure. Also that the 
primitive foliar organ possessed radial symmetry of construction 
and that the dorsiventral character is a secondary one. And this 
for the reason that the primitive leaf was a terminal organ. The 
former we see still retained in the sporophylls of Ginkgo, the female 
sporophylls of Bennettites and of Conifers and Gnetacese; in these 
last two the leaf has actually become reduced to a sporangium, 
thus strikingly resembling the far-back ancestor. It appears to be 
a mathematical necessity (as we have recently learned) for all 
lateral foliar appendages laid down on an axis to assume a dorsi¬ 
ventral, bifacial structure quite apart from any consideration of 
function in connection with light, &c. 
Another conclusion follows from this doctrine, viz., that 
sporangia are not organs sni generis, as Bower and others suppose, 
but are parts or segments of the primitive leaf; and, as we know in 
the case of pollen-sacs and ovules, may become transformed into 
ordinary vegetative tissue. Also we see the same two embryonal 
quadrants which, in the Bryophyte, produce the sporogonial capsule, 
in the vascular plant producing purely vegetative organs. 
'File primitive leaf and primitive sporangium, therefore, were 
one and the same thing, viz., the original and simple (not the 
modern, complex structures, e.g. of Polytrichnm) sporogonial capsule 
of the primeval Bryophyte. He who sees deeply and clearly enough 
