FLORIN: SYSTEMATICS OF THE GYMNOSPERMS 327 



threw fresh light on this problem from the point of view of comparative anat- 

 omy. In the ovuliferoiis scale of the Pinaceae the bundles were inverted as 

 compared with those of the bract and foliage leaf. Even the apparently single 

 cone scale of the Cupressaceae had such a double-bundle system. The conifer 

 ovules are in his opinion attached to the underside of the first and only leaf 

 of a reduced axillary shoot. This leaf, which turns its ventral side towards the 

 bract, is an open carpel representing the whole female flower. Mohl (1871) 

 regarded the double needle of Sciadopitys as analogous with the ovuliferous 

 scale of the Pinaceae, which he interpreted in accordance with Braun's origi- 

 nal conception. Strasburger (1872), on the other hand, repudiated Brown's 

 theory of the gymnospermy and believed that the conifers had female flowers 

 in the form of ovaries. These were metamorphosed buds, in which the tip of 

 the axis was changed into a nucellus. The wall of the ovary was formed by 

 two carpels fused along their margins. Both Braun (of late years) and he were 

 of the opinion that the conifer ovule is a metamorphosed shoot or flower, and 

 that the ovuliferous scale, with its ovules, constitutes an inflorescence in the axil 

 of the bract (cf. Eichler, 1875). But, abandoning his objection to gymno- 

 spermy, Strasburger later (1879a) came to regard what had been designated 

 ovaries as naked ovules. In the Pinaceae, the ovuliferous scale is a two-flowered 

 inflorescence consisting of one primary and two secondary shoots, the latter rep- 

 resented by the ovules. The female cones of this family were also dealt with 

 by Stenzel (1876), Celakovsky (1879), and Willkomm (1880), who all consid- 

 ered the conifers as gymnosperms, and the ovuliferous scale to be formed by 

 two carpellary leaves fused along their posterior margins, i.e., by the two pro- 

 phylls of a reduced and metamorphosed axillary shoot (brachyblast), each bear- 

 ing an ovule on its underside. While the problem of the gymnospermy had on 

 the whole been settled in favor of the opinion of Brown, no unanimity had been 

 reached on the structure of the female conifer cones in spite of intensive re- 

 search, a circumstance which greatly affected gymnosperm taxonomy. The mor- 

 phology of the female reproductive shoots of Ginkgo and the chlamydosperms 

 was also disputed. 



IMuch work was done in order to elucidate the formation of microspores and 

 megaspores, the development of the gametophytes, the mechanism of pollina- 

 tion, the fertilization, and the embryogeny, of the gymnosperms. Hofmeister 

 (1858) had already compared the modes of fertilization and the development 

 of the female gametophytes in several groups of vascular plants. IVIost work 

 was, however, done by Strasburger (1872, 1878, 1879a), who dealt with conifers, 

 taxads. Ginkgo, and chlamydosperms. The generally wind-borne pollen grains 

 were considered to contain the last remains of the prothallial tissue of the vas- 

 cular cryptogams and a strongly reduced antheridium. Male gametes were formed 

 in the pollen tube. He also demonstrated the reduction of the neck of the arche- 

 gonium, and its still remaining ventral canal cell or nucleus, as well as that 

 fertilization consisted in the fusion of two gametes. The fertilized egg nucleus 

 was not dissolved, as previously believed, but iiimicdiatcly began to divide to 

 form the cells of the proembryo. Strasburger presented the most monumental 

 contribution of all early workers on gymnosperm embryology. 



The general adoption of the doctrine of evolution, and the development of 

 microscopy opened a new flourishing period in the history of paleobotany. The 



