FLORIN: SYSTEMATICS OF THE GYMNOSPERMS 247 



flowers. It was generally held that the two inner of the ovnlar envelopes were 

 integuments, and that the outermost was a perianth. Quisumbing (1925) inter- 

 preted the outer integument as derived from th(^ iinier by differentiation of a 

 common primordium. Lignier and Tison (11)13) asserted, however, that the in- 

 nermost envelope is a true ovary, and that the outer two form a perianth. In 

 Pearson's opinion, the two outer envelopes of the complete, the single outer 

 envelope of the incomplete, female flower are homologous with the cupule of the 

 spike. The innermost envelope is not related to the ovary of the angiosperms. 

 The spike and the female flower are modifications of the same ]U'imitive structure, 

 which might have consisted of a terminal nucellus surrounded by a single ovu- 

 lar envelope, a ring of lateral male flowers, below which stood one or more modi- 

 fied leaf -pairs. Thompson (1918) demonstrated that the vessel, with a single 

 large performation in its end wall, is evolved by the enlargement and fusion of 

 several bordered pits, while the angiospermous vessel originates from the type 

 with many long and narrow sealariform perforations. 



The position of the Gnetales remained almost as obscure as it was at the be- 

 ginning of the twentieth century. They were regarded as derived from primi- 

 tive conifers by some authors, from the bennettites by others. Their supposed 

 angiosperm characters were sometimes strongly emphasized, but the majority 

 of botanists retained the Gnetales as an advanced and aberrant group of the 

 gymnosperms, and considered its three recent genera to represent diveruont 

 evolutionary lines of some unknown ancestrv. 



Classification of the Gymnosperms 



The gymnosperm systems published in the period under review reflect the 

 differences of opinions on the affinities of certain groups. One type of scheme 

 corresponds to the system of Engler (1892), in which the gymnosperms were 

 divided into several equivalent classes ("Wettstein, 1924; Engler and Gilg, 1924; 

 Pilger, 1926; Zimmermann, 1930, etc.). Wettstein excluded the pteridosj^erms, 

 and Zimmermann combined the Cycadales and Bennettitales in the class Cycado- 

 phyta. The other type of system is characterized by the classes being united 

 into taxa of higher rank. Jeffrey (1917), and after him Conard (1919), di- 

 vided the gymnosperms into Archigymnospermae and Metagymnospermae (Coni- 

 ferales, Gnetales). Berry (1917, 1920) substituted foi- the G.\Tnnospermae three 

 groups of equivalent rank, viz., Pteridospermophyta, Cycadophyta, and Coni- 

 ferophyta. Chamberlain (1920) proceeded on similar lines, but referred the 

 pteridosperms to the Cycadophyta. Sahni (1920) distinguished between the 

 megaphyllous Phyllospermae with leaf-borne seeds (pteridosperms and cycads), 

 and the microphyllous Staehyspermae with stem-borne seeds (cordaites, ginkgoes, 

 taxads, and conifers), ])ut left the classification of the Bennettitales and Gne- 

 tales open. Van Tieghem and Costantin (1918) and Chodat (1920), finally 

 adopted a partly different terminology. The former divided the gjnnnosperms 

 into four classes, viz., (1) Pteridospermae, (2) Natrices (Cycadineae, Ginkgoi- 

 neae), (3) Vectrices, and (4) Saccovuleae; while Chodat made the Saccovuleae 

 (=chlamydosperms) into a higher unit equivalent to the gymnosperms. Berry 

 designated Gymnospermae a taxonomic term that had outlived its usefulness 

 for other than descriptive purposes, while Hutchinson (1924) discarded the 



