﻿EXISTING AND FOSSIL CYCADS COMPARED. 



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fertilization, much as in the ferns. But contrariwise, a much smaller if not rudi- 

 mentary pollen tube is supposable. 



The megasporophylls of the genus Cycas, as organized into the large terminal 

 strobilus, are once-deflexed, not unlike the staminate fronds of Cycadeoidea. They 

 are of unique and extreme interest as the most primitive of all reproductive struc- 

 tures in any existing spermaphytes, and unquestionably indicate, independently of 

 the absolutely convincing collateral evidence afforded by the Cycadeoidete, that the 

 common history of the sporophylls of all the Cycadaceae is that of metamorphosis 

 from fertile leaves of ancestral Marattiaceous ferns by way of cycadofilicineau types 

 like Lyginodendron. The leafy features are quite clear in C. revoluta, in which the 

 basal portion bears three or more pairs of adnate ovules in the pimmlar position, 

 and the broad to laminiform terminal portion numerous thickly-haired pinnules. 

 In the closely related species C. Steenstrupi, from the Atane Cretaceous of Green- 

 land, the pinnules are not so clearly present, the broad tip apparently being thickly 



Fig. 1 26. — Characteristic forms of existing cycadean megasporophylls. 

 A. Cycas revoluta ; B. C. circinalis; C, C. Normanbyana ; D. Dion edule: E, Macrozamia Fraseri ; F. Zamia integrifolia ; G. 

 Ceratozamia mexicana. F and G. natural size ; the other forms variously reduced. tFrom Engler und Prantl. after Sachs (A). 



(C) F. V. Muller, <E) Miquel, (Ft Richard.) 



set by very long almost ramentum-like hairs. In C. circinalis the general form is 

 quite similar to C. revoluta and C. Steenstrupi, except that the pinnules of the quite 

 laminar extremity of the frond are reduced so as to form simply a serrate edge. 

 From these larger carpophylls there is a gradual reduction to forms like C. Norman- 

 dyana, with a broad, elongate tip and a single basal pair of ovules, closely paralleling 

 Dion, which has the least redticed form of carpellary leaf to be seen in the distinctly 

 cone-bearing cycads. In the other genera, much more reduction has occurred, 

 the form being quite scale-like or pedicel-like, with a terminal hexagonally 

 peltate expansion, to which is attached interiorly and laterally a pair of ovules, or 

 abnormally one or three ovules. The outer surface of the scale may be pubescent, 

 and, in Ceratozamia, bears, similarly to the staminate cones, the pair of lateral 

 horns from which this genus takes its name. 



The ovules of the cycads are throughout sessile and orthotropous, with a heavy 

 tripartite walled integument and slight prolongation of the micropylar tube. As 



