184 THEORY OF RECAPITULATION 
leaf-tip which supplies the apex of the new bud, but from a position near 
it upon the convex side of the mother-leaf. As Goebel remarks, this finds 
its parallel in the formation of the embryo and in the apogamous origin of 
a Fern-plant on a prothallus. Through such examples we arrive at a con- 
ception of a leaf also as a part which may be at times of independent 
origin, and not necessarily produced from a pre-existent and obvious axis. 
But the cases above quoted from mature plants are almost certainly 
secondary, and are probably consequent upon peculiar conditions of life. 
The question then presents itself whether the independent origin of a leaf as 
it is seen to occur in certain embryos is not also a secondary condition in 
descent, and a consequence of what might be called anticipatory develop- 
ment of that part of the shoot, to meet such early biological needs as that 
of assimilation or of storage? It is impossible to answer such a question 
with any approach to proof: nevertheless the case of A. Edgworthi is 
very suggestive of such a 
detached and anticipatory 
development of an indivi- 
dual part. Clearly the early 
appearance of a leaf in the 
Fern-embryo would be an 
advantage, while the axis 
is in no way essential for 
the performance of its first 
functions. If such be the 
origin of the first leaf or 
leaves of a sporophyte em- 
bryo, then so far from their 
Fic. 94. * 
Adiantum Edgworthi. Origin of leaf borne buds. I.=apex of 
leaf seen from above: the apical cell has divided by a cross- 
wall. xX position at which the first leaf of the bud arises. _/=posi- 
tion of origin of the lateral leaf-series whence usually in A leaf the 
pinnules develop. II. Apex of leaf seen from the side, lettering the 
same. III. Apex of leaf in optical longitudinal section : s=divided 
apical cell; J=first leaf of the bud. IV. Somewhat older stage. 
V. Apex of leaf in longitudinal section : s=apex of bud surrounded’ 
by scales ; 5=first leaf, looking like the continuation of the mother- 
leaf; w=incipient root. I.-IV. highly magnified. V. less highly 
magnified. 
independent position being, 
as is usually assumed, the 
primitive position, it would 
be secondary, a mere result 
of adaptation to the early 
requirements of the em- 
bryo. This question will 
be specially studied later 
in connection with the 
embryogeny of the Lycopods, a family in which the diversity of character 
of the prothallus has imposed considerable and instructive differences of 
development upon the embryo. Meanwhile I see no sufficient reason, on 
the ground of their position or the mode of their origin, to regard the 
“cotyledon” or “protophyll” as representing a category essentially apart 
from foliage leaves:! nor does the apparently independent existence of 
1Goebel, Organography, ii., p. 400, remarks specifically for Pteridophytes that the 
cotyledons ‘‘are without exception arrested forms of foliage leaves”- he extends the 
conclusion also to Seed-plants (p. 402). 
