EVOLUTIONARY TENDENCIES AMONG GYMNOSPERMS 41 5 



are relatively very recent. Of course it may be discovered that the 

 Cordaitales included also forms with simple strobili on leafy shoots. 

 This possibility is further emphasized by the fact that the ovulate 

 strobili of the Araucarineae, and of their allies the Podocarpineae, 

 are simple. The former tribe is a very old one, and its connection 

 with the Cordaitales is either direct or nearly so, so that it is altogether 

 probable that such ovulate strobili occurred in that group. The 

 connection of the Taxineae with the Cordaitales, however, appears 

 to be so remote, and their relation to groups with compound ovulate 

 strobili seems to be so much more immediate, that it is more reason- 

 able to suppose that their ovulate strobiliferous branches have arisen 

 from compound strobili in the way described above. 



Long after the Cordaitales had established their simple staminate 

 and compound ovulate strobili, strobili appeared in the cycadophytc 

 phylum, being found in Bennettitales and Cycadales; and even in 

 the living Cycas the loose ovulate strobilus retains the evidence of 

 its origin from the separated sporophylls of Cycadofilicales. The 

 cycadophyte strobilus has always been simple, and this may be related 

 to the more compact habit of body, with its lack of free branching. 

 The most remarkable feature of the early strobili of this phylum, 

 however, is their bisporangiate character, the two sets of sporophylls 

 holding the same relation to one another that is held by the stamens 

 and carpels of angiosperms; and this marks the Bennettitales as a 

 unique group among gymnosperms. The monosporangiate tendency, 

 however, which characterizes the coniferophytes, is shown by the 

 Cycadales among cycadophytes, and it was either established directly, 

 or it arose from an early differentiation of the bisporangiate strobilus 

 of the Bennettitales. The evidence of history favors the latter view, 

 but the probabilities of the situation favor the former. In any 

 event, both monosporangiate and bisporangiate strobili were estab- 

 lished among cycadophytes. 



THE STAMEN 



Among gymnosperms the stamen may be regarded as a very con- 

 servative structure, retaining throughout most of the phyla its fernlike 

 characteristics. Its form perhaps became almost as much differ- 

 entiated among the Cycadofilicales as it ever became among gymno- 



