Young Floral Structures. 619 



further significance attaches to Gnetopsis because one or 

 more of the three or four seeds may abort, proving, if 

 further proof were needed, how easily the monovarian 

 condition is reached. 



It is thus seen that the known facts indicate for the 

 ancient plants, especially those of Carboniferous and 

 even earlier time, wide cycles of change in both bi- and 

 unisexual fructification, as well as in all types of floral or 

 pseudovarian envelopes. That in the course of geologic 

 time cupules often resulted from the fusion of sterile 

 organs, is assumed. But that reduction of a staminate 

 disk a little beyond the growth stage seen in fig. 1, 

 coordinately with cone reduction to the monovarian con- 

 dition, would result in features such as are presented by 

 ancient seed types, is a fact of extraordinary interest. 

 That the fusion of a Lagenostoma-like cupule with an 

 inner ovarian envelope could result in the bundle sup- 

 plied outer integument of amphivascular Cycadeous 

 seeds is a reasonable suggestion; and that a disk become 

 sterile could also assume such a secondary function is 

 just as reasonable. Moreover the change could take 

 place, as geologic time goes, almost instantaneously. 

 The fact that some of the largest known gymnosperm 

 seeds are also the earliest and most complex ought to 

 have weight with botanists who regard with doubt the 

 theory of secondary and complex origin of testal struc- 

 tures, and see no analogy between seed and flower. 



In any study of the origin of seed coats one of the 

 oldest and best known critically important types is 

 Pachytesta, represented by the two species incrassata 

 and gigantea, so superbly illustrated by Brongniart in 

 the closing plates of his "Graines Fossiles Silicifiees." 

 The Pachytestas are not only amongst the oldest of 

 known seeds but striking because of their great size, 

 symmetric radiospermy, and highly developed amphivas- 

 cularity. The inner envelope is fully as complex as that 

 of various .endotestal seeds ; while the outer envelope is 

 entirely free and has a bundle system virtually as com- 

 plex as that of a cycadeoid disk. It is even apparent 

 that the inner envelope exhibited some apical division. 

 The bundles of both envelopes have marked development 

 of scalariform tracheids, uniformly present in ancient 

 seed bundles and in the Cycadeoid peduncles and many 

 ancient parent stems. 



