﻿BISPORANGIATE AXES. 143 



the important structural unit in this new type of fructification was a true staminate 

 frond, and it was also concluded that while the staminate disk surrounding an ovu- 

 late axis indicated primarily an evolution terminating, so far as then possible to 

 trace, in the gymnosperms, the juxtaposition of parts was essentially augiospermous 

 as well ; although this latter conclusion had been foreshadowed by Saporta on the 

 basis of the fact that the ovules of forms like Bennettites were embedded in a coherent 

 pericarp of expanded tips of interseminal scales. This was, then, the first time that 

 reasonably conclusive evidence was offered concerning forms suggesting a possible 

 method of reduction by which augiosperm evolution could have proceeded from a 

 pteridophytic and indeed a filicinean ancestry ; it being obvious that further reduc- 

 tion and specialization of parts in some such generalized type like the bisporangiate 

 strobilus of Cycadeoidea could result in a bisexual augiospermous flower. Lirio- 

 dendron, it was suggested for the sake of a definite point of view, might perchance 

 have been in this way derived from some separate and remote filicinean ancestry. 



ORGANIZATION OF THE BISPORANGIATE STROBILUS OF THE CYCADEOIDE/E. 



MATERIALS. 



The well-known structureless casts and imprints of dissociated Williamsonia 

 disks, as now seen to agree with the silicified forms here discussed, are likely to be 

 met with wherever plant-bearing strata of Mesozoic age occur on the globe. But, 

 with the sole exception of the pollen-bearing fruit of Cycadeoidea etrusca, all the 

 cycadeoidean material exhibiting male fructification with structure preserved has 

 been derived from three much-restricted localities in the Black Hills. These are the 

 "rim" hills, northwest of Sundance, Wyoming, and the Black Hawk and Minne- 

 kahta localities in South Dakota. From the first of these points only a single 

 specimen has been obtained. From the Black Hawk locality have come several 

 pollen-bearing Cycadeoidea Jenneyana trunks, and the type of C. ingens, as men- 

 tioned above; but the great majority, as well as the best preserved forms, are from 

 Minnekahta. In all, about twenty-five trunks with one or more unexpanded and 

 nearly mature polleu-bearing fruits are known, and the writer has had the oppor- 

 tunity to examine with more or less thoroughness all of this material. Fortunately 

 too, nearly all the fruits illustrating staminate growth in the Cycadeoidea? are 

 preserved with an exquisite beauty and fidelity of detail that yields the most accu- 

 rate and vivid conception of the organization of these long-extinct floral types, as 

 well as of the appearance they must have presented in life when maturing on 

 their parent trunks in the late Jurassic and early Cretaceous forests. 



As described in the present chapter, the bisporangiate strobilus of Cycadeoidea 

 as found in the silicified condition is borne on a short peduncle laterally emergent 

 between the old leaf bases, and consists in a central and terminal ovulate cone, a 

 surrounding hypogynous staminate disk of basally adnate, once-pinnate, synangia- 

 bearing fronds and an outer series of hairy overlapping and inclosing bracts. It 

 is next in order to take up the detailed study of these several features as observed 

 in the best conserved forms, namely, the wonderfully preserved and abundantly 

 represented male inflorescence of Cycadeoidea dacotensis. Afterwards other stami- 

 nate forms will be described. 



