326 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



cells in a single radial row all derive from the same mother cell. He described 

 in detail the development of these cells and the lignification of their walls, the 

 structure and development of the bordered pits of the tracheids, the way in 

 which the resin canals are formed, and the structure of the early and late wood. 



Other contributions to the knowledge of gymnosperm anatomy concerned 

 the mode of formation of new cells in meristems and the arrangement of their 

 walls; the origin of primary xylem and phloem; the tracheids in primary and 

 secondary wood and the nature and development of their pitting; the secondary 

 phloem; the stomata, transfusion tissue, secretory organs, and crystalline de- 

 posits of calcium oxalate in leaves, etc. Attempts had earlier (Goeppert, 1850} 

 been made to utilize the characters of the secondary wood as an aid in charac- 

 terizing conifer genera, but systematic plant anatomy did not become a more 

 prominent branch of botany until in the 1870 's. The most important work in 

 this field is C,-E. Bertrand's (1874) comparative study of stem and leaf anat- 

 omy. The anatomy of vascular plants in general was siunmarized by De Bary 

 (1877). 



As to the reproductive organs, the interpretation of the morphology of the 

 male flowers generally met with no great difficulties. The pollen grain was recog- 

 nized as a microspore, the pollen sac as a microsporangium, the "stamen" as a 

 microsporophyll (Warming, 1873, 1877), and the aggregation of microsporo- 

 phylls on an axis as a flower (Eichler, 1863; Strasburger, 1872). Opinions dif- 

 fered, however, on the male flowers of the Gnetaceae (Strasburger, 1872; McNab, 

 1873; etc.). This applies even more to the female organs — except to those of 

 the cycads, which were interpreted as single flowers with ovules marginally 

 attached to open carpellary leaves (Miquel, 1869; Tieghem, 1869; Braun, 1876; 

 Warming, 1877). The conifer cones in particular were debated. Their correct 

 interpretation was considered an essential prerequisite for a determination of 

 gymnosperm relationships. 



The axillary ovuliferous scale of the Pinaceae was in Braun 's (1860) opinion 

 a fertile, two-leafed short shoot or flower with the leaves fused along their pos- 

 terior margins. Taxus and Ginkgo lacked ovuliferous scales. The Araucaria cone 

 scale was formed by the fusion of a single-leafed short shoot to the bract, while 

 the flower of the Taxodiaceae, and probably also of the Cupressaceae, had sev- 

 eral small leaves fused together and to the bract. Baillon (1860, 1864) defi- 

 nitely opposed Brown's thesis of the gymnospermy of the conifers and taxads. 

 According to Baillon the female flower is either terminal, or placed in the axil 

 of a bract or leaf, but always borne on an axis. It is not gymnospermous, but 

 possesses two carpels and a naked ovary containing an erect, orthotropous ovule 

 upon a basal placenta. Baillon 's account was criticized by Caspary (1860), who 

 interpreted the so-called ovary as an ovule, the two "carpels" as a two-lipped 

 integument, and the ovuliferous scale of the Pinaceae as formed by the two 

 first leaves of an axillary short shoot fused along their anterior margins. Eich- 

 ler (1863) attributed to the naked ovules of the conifers a single, or sometimes 

 double, integument. The ovules were in certain cases covered by an aril, but 

 never by an ovary or a perianth, and they were borne in the axils of small leaves 

 on a rudimentary short shoot, placed in its turn axillary to a bract. Sachs 

 (1868), however, wanted to regard the ovuliferous scale of the Pinaceae as an 

 excrescence on the bract, and the bract as a carpel. In 1869 van Tieghem 



