858 



SCIENCE 



[N. S. Vol. XXV. No. 648 



9. Dakota Formation of Kan- 

 sas Oyeadeoidea, 1 



10. Pre-Laramie (?) of Golden, 



Colo Cycadeoidea, 1 



From this it may be observed that up to the 

 present it is possible to recognize 



Species. 



Oycadeomyelon 1 



Cyeadella 21 



Cycadeoidea 40 



with one specimen as yet unidentified. 



The author discusses at some length the 

 varying conditions of fossilization and the re- 

 sulting effect upon structure; and he further 

 directs attention to the alterations of external 

 form due to pressure, either during or after 

 fossilization. The cutting of such bulky ma- 

 terial, and more particularly the excision of 

 special parts, required the elaboration of spe- 

 cial methods and the manufacture of specially 

 constructed cutting tools; but the exercise of 

 ingenuity, skill and great patience enabled tha 

 author to cut all his own sections with great 

 success. 



As in existing cycads, the fossil forms show 

 a highly developed armor composed primarily 

 of the persistent leaf bases; but in addition 

 there is a ramentum which is borne over and 

 densely packed between the leaf, peduncle and 

 bract surfaces, as well as thickly enveloping 

 the entire crown. The presence of such a 

 ramentum is well known, not only in the 

 cycads, but also in the ferns. The special 

 features of this structure in the present case 

 are, first, the perfection of its preservation, 

 probably resulting from the free percolation 

 of silica-laden solutions through the hairy 

 ramental mass; and second, the fact that 

 among fossil species the ramentum shows a 

 profuse development which is in striking con- 

 trast with its very reduced condition in exist- 

 ing species, and which in Cyeadella results in 

 fully half the bulk of the trunk being made 

 up of this material. This variation, while at 

 first appearing to constitute the basis of a 

 broad differentiation of the great groups, is in 

 reality little more than of generic importance. 

 The various stages of development found show 

 conclusively that the Cycadeoideae and Cyca- 



dacese have been alike subject to a progressive 

 reduction of the profuse ramentum character- 

 izing their common Paleozoic filicinean an- 

 cestry.. 



The most striking external feature of all 

 the cycads is to be found in the armor com- 

 posed of spirally arranged old leaf bases. In 

 existing cycads the regular order in which the 

 leaves appear is not disturbed except by the 

 appearance of terminal cones. In Cycadeoi- 

 dese, on the other hand, disturbance of this 

 arrangement is very common and is due to 

 the emergence of numerous large and laterally 

 borne fructifications, and to the particular 

 level at which periderm formation takes place. 

 In consequence of these disturbances, the leaf 

 arrangement can not be used for either gen- 

 eric or specific distinctions. A much more 

 definite and constant feature is to be found in 

 the particular grouping of the vascular bimdlea 

 in the leaf scars. 



Special interest centers in the character of 

 the inflorescence. A study of the ovulate cone 

 of Cycadeoidea wielandi shows a structure 

 which arises from between the old leaf bases 

 or else from their axils in part, at any point 

 between the base of the trunk and the youngest 

 series of leaves. In structure they present the 

 type exhibited by Bennettites gihsonianus and 

 B. morierei. But it is found that in all the 

 strobili, situated about the lateral bract-bear- 

 ing surface of the peduncle, and just beneath 

 the terminal ovulate cone, there is an annular 

 shoulder which bears distinct traces of some 

 earlier, dehiscent or abortive or wilted disk. 

 This disk is seated on the receptacle above the 

 bracts, and vascular bundles pass out to it 

 from the woody cylinder of the peduncle. 

 This disk is interpreted as a staminate recep- 

 tacle, and its presence in all the specimens 

 from the Black Hills is held to signify that all 

 these species were bisporangiate. In some 

 cases the inconspicuous character of the disk 

 leads to the inference that the inflorescence 

 was homosporous. The evidence presented by 

 the great majority of cones studied supports 

 the conclusion that all the known Cycadeoidese 

 are descended from bisporangiate forms, and 

 that of all the considerable number of fruits 



