68 ON THE SEXUAL ORGANS OF THE CYCADACES. 
already potentially determined. The final result of the formation of 
an ovule is the differentiation of one of the cells situated in its axis, 
which produces the new individual; in this way the embryo-sae is to a 
certain extent the equivalent of the parent-cell of the bud. The em- 
bryo-sac is fertilized by the absorption of matter contained in another 
cell which places itself in contact with it; and if we inquire the cause 
of the individualization of the parent-cell of a bud, it must be looked 
for also in the phenomena of nutrition, of which the adjacent parts are 
the seat.  Modificatious of the movements and distribution of the nu- 
tritive juices are the means of exciting the production of buds. The 
destruction of a terminal bud causes the production of numerous lateral 
ones. Incisions, by accumulating the supply of food at particular 
points (of a leaf or root, for example) cause the production of buds 
there. The ovule is usually considered as distinct from the carpel, and 
the line of separation drawn at the origin of the funicle; but would it 
not be more philosophical to regard it as a stage in the development 
of a particular part of the carpel, and to look upon the embryo-sac 
alone as a new and independent structure ? 
The search amongst monstrous structures for the key to the true 
meaning of the parts of the ovule is a proceeding which encounters 
serious difficulties in the circumstance that the parts are very frequently 
so altered in position and form as to be scarcely recognizable with suf- 
ficient certainty. The normal organogeny of carpels and ovules, which 
has been chiefly studied in Angiosperms, supplies good information as 
to the external aspects of the phenomenon, and reveals to the eye its 
anatomical characters, but it will always be extremely difficult to pene- 
trate in this way into the morphological interpretation of organs re- 
duced to their minimum of development. Besides Pi the complete 
history of the evolution of the leaf is still wanting; even after the 
admirable researches of Eichler, it has not been distinctly ascertained 
in all its bearings. Under these circumstances the consideration of 
the carpophylls of the Cycadacez, which are less modified by metamor- 
phosis than the corresponding organs in all other Phanerogams, will 
perhaps supply Some explanation as soon as their development has 
been completely studied,—a labour for which unhappily the materials 
cannot be obtained, except in the native country of the plants. 
I have consequently confined myself to calling attention to the fol- 
lowing points :— 
