﻿l62 



REPRODUCTIVE STRUCTURES. 



we might on theoretical grounds declare was present in the Cycadeoidea; ; for the 

 pollen grains being of markedly larger size than those of modern cycads, but not 

 nearly so large as those of Cordaztes, and being borne on frond derivatives, little 

 else than a strictly intermediate stage of prothallial elimination could be surmised. 



CYCADEOIDEA HELIOCHOREA. 



Certain fragments of large trunks from the northwestern Black Hills Rim 

 referred by Professor Ward to a distinct species (C. heliochorea) are found to pre- 

 sent the same structural characters and essentially the same stages of fructification 

 seen in the foregoing specimens of C. dacotensis, to which species they might 

 justly be referred. Of these fragments, specimen 726 bears a bisporangiate strobilus 

 agreeing not only in structure and stage of growth with fruits I and III of specimen 

 214 (C. dacotensis), but affording, as the result of the eroding away of all the middle 



portions of the rachides of the staminate 

 fronds, a most clear supplementary illustra- 

 tion of the main features of cycadeoideau 

 sporophyll distribution and the manner in 

 which the synangia are borne. The former 

 position of the rachides of the fronds is 

 indicated on the outer and upper portion of 

 the mass of synangia by deep longitudinal 

 furrows, at the sides of which the points 

 of sporophyll attachment may be readily 

 determined. Many of the synangia stand 

 out in full relief as slightly arcuate bodies 

 plainly attached sub-laterally to the spor- 

 ophylls in pairs in the manner already 

 described (see fig. 86 and photographs 2 and 3, plate xlv). A transverse section 

 cut through the mass of synangia still attached to the sporophylls, and well above 

 the central ovulate cone, is shown in figure 85. 



CYCADEOIDEA INCENS AND C. JENNEYANA. 



The robust trunks of Cycadeoidea ingens and the taller columnar forms referred 

 to C. Jcnncyana, represented by many magnificent specimens from Black Hawk, 

 bear bisporangiate strobili of the same general type and structure as those of C. 

 dacotensis, although the disks are divided up into fewer fronds. In C. ingens twelve 

 or thirteen, and in a strobilus referred to C. Jenneyana only about ten fronds are 

 present. But any such slight numerical variation would probably not in itself con- 

 stitute a difference of specific value — certainly not if a distant analog)' is afforded 

 by Zamia floridana, in which the ranks as well as the number of sporophylls in 

 each rank vary noticeably in both the staminate and the ovulate cones. Other differ- 

 ences are present, however. Aside from the lesser uumber of the fertile fronds, the 

 strobili of the two species before us do not exhibit markedly different structural 

 features from those already described in the better conserved strobili of C. dacotensis. 



Fig. 86. — Cycadeoidea dacotensis. X 6. 



Synangia partially exposed by weathering out in their natural posi- 

 tion near the surface of the strobilus shown in transverse section 

 in the preceding figure. The palisaded synangial walls are 

 mostly split off, thus leaving in full view the rows of elongate 

 pollen-filled sporangial sacs. 



