362 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



Florin (1936a) revised the fossil ginkgophytes and proposed a tentative clas- 

 sification based on the morphology and epidermal structure of the foliage leaves 

 (see also Harris, 1932-1937). Certain genera were studied in respect to the leaf- 

 traces in their short shoots and the internal structure of their leaves. Two groups 

 were discerned, a smaller with petiolate leaves of the Ginkgo type, and a larger 

 with wedge-shaped leaves. The latter also differed in the division of the leaves, 

 in the short shoots being deciduous, in having single leaf -traces, etc. The origin 

 of the double leaf-trace in living Ginkgo, as described by Gunckel and Wet- 

 more, tends to emphasize the differences between the two groups. The female 

 flowers of a permian ginkgophyte, Trickopitys, were found to resemble those of 

 Ginkgo in position and general type (Florin, I.e.). Krausel (1943a, 1943b) re- 

 investigated some mesozoic forms, among which was a species of Sphenohaiera 

 with male flowers on short shoots. Their axis is branched into stalklike, bifur- 

 cated appendages, carrying erect sporangia terminally. Harris (1942-1952, 

 1951b) became increasingly doubtful of the correctness of classifying the genera 

 Czekanoivskia and SoJenites in the Ginkgoales. On circumstantial evidence he 

 referred to these a type of female fructification, Leptostrohus, different from 

 that of any known plant. The larger of the above-mentioned groups of ginkgo- 

 phytes might thus turn out to be a heterogeneous assemblage. 



The Ginkgoales and Cordaitales are probably of a common origin very far 

 back in the history of the vascular plants. 



CONIFERAE 



New efforts were made to solve the significant problem of the morphology of 

 the female conifer cones. At first opinions differed as much as ever. Kotter 

 (1931) and Schmid (1937) lield to the excrescence theory of Sachs-Eichler. Ste- 

 fanoff (1936) considered the ovuliferous scale a "cladosperm," homologous to a 

 dichotomized projection of a pteridosperm frond as well as to a leaf of Cycas 

 or Ginkgo. Pulle (1938) regarded the araucarian cone as uniaxial, and as a 

 primitive form of female strobilus in the conifers. Thomson (1940) agreed to 

 this, and considered the bract and ovuliferous scale components of a megasporo- 

 phyll. In Chadefaud's (1940) opinion the conifer "carpel" is derived from a 

 prototype analogous to the pinnate megasporophyll of Cycas, and composed of 

 a rachis and uniovulate pinnae. The ovuliferous scale developed by fusion of 

 the pinnae, while the main part of the sporophyll formed the bract. Kujala 

 (1942) and Hiitonen (1950) embraced the foliolar theory of Delpino and Pen- 

 zig. Arber (1950) regarded the ovuliferous scale as made up of two fused leafy 

 outgrowths from the axillant bract. Hirmer (1936) and Propach-Gieseler (1936) 

 investigated the ontogeny and comparative morphology of the female cones of 

 living conifers, and arrived at the conclusion that the ovuliferous scale and the 

 bract result from a serial splitting of one single member. The fertile part of the 

 megasporophyll was believed to derive from a peltate perisporangiate struc- 

 ture. Other morphologists professed, in one form or another, the brachyblast 

 concept of the ovuliferous scale. To begin with, this applies to Sahni and Singh 

 (1931) and Doyle and O'Leary (1934), who investigated the female cones of 

 Fitzroya. The latter authors noted that the cone structure is a very ancient fea- 

 ture, the origin of which must be sought in the reduction of the primitive non- 



