pdf 25 MB - BSBI Archive

ON THE SEXUAL ORGANS OF THE CYCADACE.E. 65
Schaclit, and especially of Hofmeister, liave cleared up the history of
gymnospermous ovules, their mode of fertilization, and the develop-
ment of the embryo. The Cycadacees only remain almost completely
excluded from these investigations ; and if this may be accounted for
by the remoteness of the native country of these plants, and the rare
occasions of their flowering in our botanic gardens, it is the more to be
regretted, as their ovides are of the simplest form, and, from their size,
the best adapted for examination.
Without treating the subject in detail, I propose to notice and dis-
cuss the reproductive organs of the Cycadacea. I adopt the morpho-
logical identity of ordinary leaves with the structures which bear the
ovules and pollen as the basis of these remarks,—with this physiolo-
gical distinction between the latter, that in Cycas the male organs,
collected into a cone, arrest the terminal growth, like the male and fe-
male organs af all other Cycadacece, so that growth must be continued
by lateral buds ; while the ovule-bearing leaves in the same genus are
collected into a large terminal tuft, in the centre of which is a leaf-
bud. We have here the representative of a primitive type ; structure
and function reach their most simple expression ;
the ideal arrangement
of the organs of reproduction, which has been established in the higher
plants by the doctrine of metamorphosis, is realized in an actual ex-
ample.
In comparing different genera of the Cycadacece with one another, it
is easy to recognize the homology of the sexual apparatus. From the
carpophyll of Cycas, which retains in every respect its leafy characters,
there is a gradual passage, through Dion* and Macrozamia, to the
squamose and peltate organs of Zamia and other genera. The same
tiling holds good, as I have previously shown at greater length, with
the male organs. The male and female cones, or the terminal tuft of
carpophylls, each represent a single male or female flower, composed
merely of the simplest sexual organs, anthers, and carpels.
While the homologous organs of plants often ditter wadely, both in
their anatomical relation and in their external development, a definite
anatomical resemblance may be traced in the Cycadacece. The carpo-
* Continental authors have been in the habit of quoting Lindley's genus
Dion as having been thus spelled by error (lliq. Prod. Syst. Cyc. p. 22; " Dioon,
DC. Prod. xvi. 2, p. 537, " Dioon (errore
Lmdl. Bot. Eeg. ubi Dion vocatur" ;
Dion)" etc.) ; but he intentionally omitted one of the o's, and invariably wrote
it Dion, and be has classical authority for thus contracting it.
—
Ed.