346 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



geological ages, their external morphology, anatomy, and taxonomy. Holliek and 

 Jeffrey (1909), Stopes and Fujii (1910), and Ogura (1930-1932) dealt with 

 the anatomy of various conifers of cretaceous age. Nathorst (1908) worked out 

 the morphology of the female cones of the early mesozoic genera Palissya and 

 Stachyotaxus, and Schliiter and Schmidt (1927) observed the double cone scale 

 of a triassic Voltzia. Wood anatomy as applied to fossil material also attracted 

 attention. A critical review of this subject was published by Krausel (1919). 



GnETALES ( ChLAM YDOSPERM AE ) 



Solms-Laubach (1908) thought that the three genera of the Gnetaceae had 

 nothing in common, except that they were neither conifers nor cycads. 



Ephedraceae. According to Thoday and Berridge (1912) a reduction can 

 be traced in the microsporangiate shoot, from clearly bifid sporangiophores with 

 four bilocular synangia to each half, to nonbifid sporangiophores on which in- 

 creasing numbers of sporangia are fused, often forming in the process trilocular 

 or even quadrilocular synangia. The bipartite sporangiophore with its paired 

 bilocular snyangia appeared to them to be homologous to the bipinnate micro- 

 sporophyll of Cycadeoidea. Coulter and Chamberlain (1917), however, consid- 

 ered it an axial structure. In Pearson's (1929) opinion the male flower is a 

 greatly reduced strobilus consisting of an axis bearing two pairs of appendages 

 and the sporangiophore itself. The female flower was regarded as a specialized 

 bud, generally axillarj^, but sometimes terminal in position. The vascular 

 anatomy of the vegetative organs was investigated by Thompson (1912) and 

 Jeffrey (1917). Diffuse and abundant parenchyma, vessels, and large rays, are 

 characteristic features of the secondary wood. The tracheary pitting is similar 

 to that of the conifers. The vessels are composed of tracheidlike segments, which 

 have bordered pits in their radial walls, crassulae, tertiary spirals, and trabe- 

 culae. Perforations are formed on the oblique end walls by the initial enlarge- 

 ment of the bordered pits, by the subsequent loss of both torus and border, and 

 often by the fusion of such contiguous perforations. Bailey (1925) stated that 

 the primary xylem is of a highly modified type, and that there is no accurate 

 record of successive structural changes in the evolution of the circular bordered 

 pit in the inner zone of transitional tracheids. 



Welwitschiaceae. The male (pseudohermaphrodite) flower was generally re- 

 garded as approaching most closely the primitive floral organization of the Gne- 

 tales, from which Ijoth the male and the female flowers may be derived (Pearson, 

 1929). The opinions of the homologies of the various parts of these were sum- 

 marized by Lignier and Tison (1912). Church (1914) believed that the flowers 

 were originally hermaphrodite, and that the functional ovulate flower represents 

 an advanced stage of reduction. Sykes (1910a, 1910b), Lignier and Tison, 

 and Church, contributed to the unraveling of the vascular anatomy of the 

 flowers and ovules. The structure of the inflorescence axes is extremely com- 

 plex, the bundles being arranged in two more or less definite series, and re- 

 calling to some extent, like the structure of the adult stem, the vascular anatomy 

 of the Medullosaceae. 



Gnetaceae. According to Pearson (1929) the difficulty of interpreting the 

 inflorescences is due to pecularities in the position and organization of the 



