. Morphology of gymnosperms. Gymnosperms; Plant morphology. GINKGOALES 197 bearing several ovules and terminating in a scaly bud (fig. 225). In 1900 Seward and Gowan (28) reviewed the whole situation, studied additional abnormalities, and coincided with the conclusions of Fujii. And now Shaw (50), investigating the vascular anatomy of the strobilus, dissents from the current view that the collar is a much reduced megasporophyll. It seems that the bundles of the collar show inverse orientation, and a corapsLxisonrnth. Lagenostoma sug- gests that the collar of Ginkgo is a vestige of the cupule t
. Morphology of gymnosperms. Gymnosperms; Plant morphology. GINKGOALES 197 bearing several ovules and terminating in a scaly bud (fig. 225). In 1900 Seward and Gowan (28) reviewed the whole situation, studied additional abnormalities, and coincided with the conclusions of Fujii. And now Shaw (50), investigating the vascular anatomy of the strobilus, dissents from the current view that the collar is a much reduced megasporophyll. It seems that the bundles of the collar show inverse orientation, and a corapsLxisonrnth. Lagenostoma sug- gests that the collar of Ginkgo is a vestige of the cupule that in- vested seeds of the Lagenostoma type. This claim for the cupule nature of the collar is most in- teresting, and if it is the true one, it even more strongly emphasizes the close connection of Gink- goales and Cycadofilicales. The evidence at present sug- gests that the structure under discussion is a strobilus bearing two or more megasporophylls, which are usually reduced to the so-called "collars," but which sometimes resume their original leaflike character. These ab- normal ovuliferous leaves are most suggestive of the ovulif- erous leaves of the Cycadofilicales, and hence of the origin of the ovulate strobilus of Ginkgo. While the stalk of the strobilus re- sembles the petiole of a leaf, it is quite different in its structure. A transverse section of a petiole shows the two bundles already mentioned as representing the double leaf trace; while a trans- verse section of the stalk of a strobilus shows the four bundles which would be expected in a stem bearing two leaves (collars) at its apex (figs. 226, 227). When more than two ovules are borne on one stalk, there are twice as many bundles in the stalk as there are ovules at its apex, just as there should be if each collar were a mega-. FlG. 224.—Ginkgo biloba: axis bearing seven ovules, each with a pedicel.—After Sprecher (47).. Please note that these images are extracted from scanned page images that m
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