﻿240 RELATIONSHIPS. 



10. Development of sori as in Marattiaeeous forms, and fern-like initial stages of 

 megaspore. 



1 1. Tendency of sporangia of Cycas to form Angiopteris-Viks. sori. 



12. Marattiaeeous structure of the S3 7 nangia of Cycadeoideae. 



13. Retention of megaspore membrane in both the Cycadaceae and Cycadeoideae. 



14. General equivalence of the megaspore to monangial sorus. That is, com- 

 pared with the vascular cryptogams the ovule is a megaspore, the integument an 

 indusium, and the entire seed therefore a monosporic sorus, with the embryo sac as 

 analogue of a megaspore, the endosperm of the prothallus, and the archegonia of the 

 corpuscula. 



15. Similarity in vegetative and reproductive features to the members of the vast 

 Paleozoic complex of seed- bearing "quasi-ferns." 



Plainly the preceding resume of the principal characters of the two great cycad 

 groups as combined and showing their descent from Marattiaeeous ferns of the 

 Paleozoic, is not merely conclusive, but one of the great cornerstones upon which 

 the conception of evolution can rest secure. Nevertheless, investigators must 

 doubtless, for a long time to come, very naturally differ greatly in their view of the 

 degree of vegetative and reproductive complexity theoretically reached by the com- 

 mon ancestry of the Cycadaceae and Cycadeoidece. For not only will the knowledge 

 of the facts bearing on this most interesting problem be greatly augmented, but 

 those facts already known have been gleaned by many investigators; and different 

 students very naturally observe differently, or may study the different classes of 

 evidence falling within their ken in differently accentuated manner. So far as 

 the writer is concerned, however, he has already made it clear in the closing pages 

 of the preceding chapter that he regards the productive and vegetative parallelism of 

 the two great cycadalean orders as fundamentally ontogenetic rather than homo- 

 plastic, whence a comparatively modern rather than an ancient separation of the 

 groups appears in his immediate perspective the more plausible. 



For the sake of specific clearness it may be added that we may well conceive 

 of two closely related Marattiacean genera, one with sori of the Angiopteris type, 

 and the other with synangia like Marattia, undergoing a series of parallel changes 

 not completely chronologic, and giving respective and separate origin to the 

 Cycadeoideae and the Cycadaceee. In such a ease the main point is that this pair of 

 hypothetical ancestral genera must have retained complementary family relationships 

 after the assumption of the primitive cycadaceous form. But of such finer grada- 

 tions of homoplasy we can have but a vague and nebulous idea, and it must be 

 pleaded that it affords a clearer conception of morphologic and biologic relation- 

 ships to regard the ancestors of the Cycadeoideae as integrally cycadean, or perchance 

 cycadofilicinean, rather than simply Marattiaeeous. In fact, the more distant 

 relationship to Ginkgo and Cordaitcs would at best leave to the latter conception 

 little of probability. 



While with increasing knowledge of the paleontologic record, origins are ever 

 being found more ancient and homoplastic relationships more omnipresent than 

 at first apparent, those who would widely separate the Cycadeoideae from the 

 Cycadaceae on the basis of either origin or form may well pause to consider how 

 extremely complex the changes from ferns to existing spermaphytic lines must have 

 been, and how correspondingly small are the chances for long-persistent parallelism. 



