328 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



most prominent paleobotanists of that time were Williamson and Eenault. From 

 1871 onwards, Williamson published a long series of important monographs on 

 the structure of vascular plants of carboniferous age. Calamites, sigillarias, and 

 lepidodendrons presented secondary growth, and were therefore thought to be 

 gymnosperms. Williamson proved, however, that this is only a subordinate 

 character, and that the said plant groups are actually vascular cryptogams. 

 Eenault, who with Williamson may be considered a founder of modern paleo- 

 botany, also devoted himself mainly to microscopic examinations of paleozoic 

 plants. In this connection his study of the cordaites (1879) attracts most in- 

 terest. In 1877 Grand' Eury had given an account of this extinct group. Re- 

 nault investigated the stem, root, and leaf anatomy, the morphology of the male 

 and female inflorescences and of the pollen, and the anatomy of the seeds (cf. 

 Brongniart, 1881). While Grand' Eury had considered the cordaites most 

 closely related to the conifers, Renault believed that they formed a separate 

 group of cycads. He also described the stem anatomy of the Poroxyleae, a new 

 group of fossil gymnosperms. 



The stems of Medullosa were investigated by Goeppert and Stenzel (1881), 

 and were believed to represent a new group of fossil cycads. Kraus (1870-1872) 

 divided recent and fossil conifer stems into five groups, viz., Araucarioxylon, 

 Pityoxylon, Cedroxylon, Cupressinoxylon, and Taxoxylon, a classification which 

 for a time became generally adopted by paleobotanists. Carruthers (1870, and 

 earlier) studied the presumed cycad genera Williamsonia and Bennettites of 

 mesozoic age, and Schenk (1867) began the microscopic study of fossil plants 

 preserved as compressions. 



Evolutionary ideas, and the results of morphological and anatomical re- 

 search, were only gradually expressed in the classification of gymnosperms. The 

 old system of A. P. de Candolle (1819) was essentialy the basis of that of Ben- 

 tham and Hooker (1880). Braun (1864) was the first to place the gymnosperms 

 as an independent group between archegoniates and angiosperms ; he distin- 

 guished three families: Cycadaceae, Coniferae, and Gnetaceae. Eichler (1880) 

 then divided the conifers into the Taxineae (including Ginkgo), Cupressineae, 

 and Abietineae. Important works on the classification of the cycads were pre- 

 sented by Miquel and Regel (Schuster, 1932). A distinguishing feature of the 

 gymnosperm systems of the period now reviewed is that the extinct fossil groups 

 are disregarded. 



The Period 1880-1900 



Ever since Hofmeister's work of 1851, the alternation of generations in cor- 

 mophytes had been in the foreground of the general botanical interest. Celakov- 

 sky (1874) had distinguished between homologous and antithetic alternation. 

 The former implied a differentiation of generations of fundamentally like de- 

 scent, while the latter was characterized by an intercalation of a new — sporo- 

 phytic — stage between successive gametophytes. Bower (1890, 1894) became 

 the chief exponent of the antithetic theory. His view was supported by the dis- 

 coveries of Overton and Dixon that the nuclei of the cells of the gametophytes 

 in gymnosperms have only half as many chromosomes as the sporophyte. Stras- 

 burger (1894) considered this difference fundamental. 



