﻿OVULATE CONES. I 25 



tion as two more or less sinuous bands of tissue ; occasionally both the nucellar 

 wall and that of the testa may be floated more or less evenly into a central position, 

 and there be more or less vaguely preserved. But fortunately in various seeds 

 collapse is only partial or has not occurred at all, the thin-walled nucellus and con- 

 tents being normally preserved. In such cases the nucellus may be quite filled with 

 large rounded and thin-walled cells, as photographed on plate xxx. Or these some- 

 times appear to surround an irregular interior cavity. In a few instances the testa 

 appears to be ruptured and some of the large interior cells have poured out and 

 then been preserved, although such rupture and preservation is not unusual in 

 silicified woods. In by no means rare instances the fully distended nucellar wall, 

 in longitudinal as well as transverse sections, is filled out to the testa with the large 

 rounded cells, the mass of tissue being irregularly, though characteristically', trav- 

 ersed by bands, which under very favorable conditions are seen to be made up of 

 small cells, possibly representing an initial stage of embryo formation. These 

 bands appear in the photograph, plate xxx, and are in nowise to be confused with 

 the megaspore membrane, which is in various instances also conserved. 



In the absence of the further sections and study so urgently required, the best 

 interpretation of the pre-embryouic stages just noted would seem to be that what- 

 ever may represent the oospore quite filled the nucellus ; and that further, as is 

 suggested by the nearly parallel condition in Ginkgo, there was no suspensor devel- 

 opment, whence embryo formation must have taken place directly from the tissue 

 here seen to fill the oospore, and thus represent a proembryo or protocorm. At 

 least this is the interpretation recently given by the writer in a brief notice of these 

 seeds, it being held that the cells are in size and general appearance proembryo-like, 

 and that it is not likely that the large-celled tissue is prothallial, since it is traversed 

 by bands or sheets apparently resulting from a division process unlike any preceding 

 archegouial formation. The preservation is so perfect that were the archegonia 

 still present when fossilization occurred, traces should appear in the seeds of the 

 cones studied. Instead, as stated, a homogeneous tissue fills the entire nucellus, 

 save that in some cases a cavity, resembling but much smaller than that of the 

 Cycas proembryo, is suggested, while the bands are better explained as a cell-division 

 marking initial embryo formation.* 



Although it has not been found possible to treat this subject on the basis of 

 a fuller series of sections at present, there is more or less certainly indicated a sug- 

 gestive analogy to Ginkgo, in which there is a much simpler form of embryogeuy 

 than in the other Gymnosperms. In this last survivor of an ancient and cosmo- 

 politan line, with various more or less distant cycadean and cordaitean affinities, 

 proembryo, suspensors, aud embryo proper are not differentiated in the oospore. 

 Instead, all these are merged together and germination of the oospore begins by free 

 nuclear division, with entire omission of suspensor development. As a resultant, 



* If perchance the tentative view adopted be wrong, and the central tissue simply prothallial, then the 

 accompanying structureless seed interiors, which are in a considerable majority, might represent a fertilized 

 series. In such alternative one might expect, however, that silicified embryos would be present in the 

 series of cones in which these delicate preembryonal cells are so well conserved, and that the latter would 

 show evidence of collapse, instead of having the appearance of normal tissue as capable of further growth 

 as any other present. 



