. Morphology of spermatophytes. [Part I. Gymnosperms]. Gymnosperms; Plant morphology. 140 MORPHOLOGY OF SPERMATOPHYTBS ovules are evidently cauline, being borne at the summit of a short bractlet-bearing shoot, which arises from the axil of a bract. As has been mentioned before, the ovules may be reduced to a soli- tary one in a strobilus, and the bracts may be very few in num- ber. Two envelops are ap- parent, and permit the same diversity of opinion as exists in reference to the ovular envelops in the Gne- tales. It seems altogether simpler to regard the two envelops in Cordaites as two integ
. Morphology of spermatophytes. [Part I. Gymnosperms]. Gymnosperms; Plant morphology. 140 MORPHOLOGY OF SPERMATOPHYTBS ovules are evidently cauline, being borne at the summit of a short bractlet-bearing shoot, which arises from the axil of a bract. As has been mentioned before, the ovules may be reduced to a soli- tary one in a strobilus, and the bracts may be very few in num- ber. Two envelops are ap- parent, and permit the same diversity of opinion as exists in reference to the ovular envelops in the Gne- tales. It seems altogether simpler to regard the two envelops in Cordaites as two integuments, although there is no tubular pro- longation of the inner in- tegument as in the Gne- tales. The nucellus devel- ops a remarkably promi- nent and persistent beak, composed of modified and heavy-walled cells, through which a passageway leads to a large pollen chamber (Fig. 96). The whole structure of the nucellus recalls the Cveads and Ginkgo, and, as is the case with them, the nucellar tissue which caps the embryo sac disorganizes, permitting the persistent beak to settle down upon the embryo sac (Fig. 91). There is also a striking resemblance to the nucellus of Ginkgo, as described by Hirase, in the fact that the endosperm develops a protuberance which supports the settling beak like a " ; Under the shel- ter of this improvised tent the archegonia are found and the male cells are discharged. The situation is so suggestive of Oycads and of Ginkgo that one can hardly escape the conviction that in the process of fertilization they are approximately the same. Traces of the archegonia have been found, so that their position is definitely determined. The ovulate structures of the Cordaitales as described above. Fig. 96.— CordiantJms Grand? Eiiri/i, showing the beak of the nucellus; wedged in the pas- sagewaj' are the large pollen grains, which show the shagreenlike surface and the in- ternal group of cells.—After Please note that these images
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