410 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



toward the goal that in the arrangement of plants the genetic evolution or at least the 

 morphological sequences express themselves (ibid, p. xvi). 



He indicated strong skepticism that angiosperms had arisen from any living 

 gj-mnosperms, that monocotyledons arose from dicotyledons or vice versa, that 

 sympetalous or apetalous families of dicots were derived from existing chori- 

 petalous ones, or even that any living or extinct family had arisen from another. 

 Instead, he devoted himself to tracing the "progressions," or evolutionary mor- 

 phological stages through which he believed the members of different family 

 stocks had advanced. The idea of a "flower" was extended downward to the 

 vascular cryptogams, and a logical sequence of naked, to apetalous, to chori- 

 petalous, to sympetalous flowers was indicated as a major evolutionary trend 

 and given great weight in his system of arrangement. 



The Englerian system has achieved wide acceptance as a basis for the ar- 

 rangement of families in manuals and herbaria, both in Germany and in the 

 United States. In England, Rendle (1904, 1925) followed it closely, but it can- 

 not be said to have displaced there the arrangement of Bentham and Hooker. 

 Wettstein (1924) likewise adhered closely to the Englerian sequence and at- 

 tempted to bring it more closely into conformity with his own ideas of phy- 

 logeny. For example, he attempted to trace a logical development of "floral 

 types" from extinct gymnosperms via Gnetalean-like inflorescences to apetalous 

 dicotyledons, to derive monocots from dicots, and to provide a logical explana- 

 tion of the change from open to closed pollination. The fact that Wettstein's 

 book has not been translated into English has doubtless militated against its hav- 

 ing a wider influence than it has enjoyed. The Stanunhaum offered by Janchen 

 (1932) provides a graphic summary of Wettstein's views on the arrangement 

 of families. 



The systems mentioned thus far agree in visualizing the angiosperms as hav- 

 ing arisen from some form of gymnospcrmous plant with unisexual strobili, as 

 having been primitively wind-pollinated, and as having developed a floral en- 

 velope of varying complexity from originally naked flowers. There is the further 

 connotation that woody, catkin-bearing dicotyledons have probably had a dis- 

 tinct origin from that of choripetalous or sympetalous groups, and that the angio- 

 spermous flower has arisen from gymnospcrmous inflorescences. 



A quite different train of development is postulated for angiosperms bj^ such 

 workers as Bessey, Hallier, and Hutchinson, who developed their respective sys- 

 tems on the foundation of the de Jussieu-de Candolle-Bentham and Hooker natu- 

 ral systems. Bessey (1897, 1915) formulated a scheme of classification of angio- 

 sperms which has gained wide acceptance in the United States as a teaching 

 device. The classification assumes that flowering plants have had their origin 

 from "cycadean strobiliferous ancestors" and that the individual flowers of 

 angiosperms have their homologues in Bennettitalean bisexual strobili. The au- 

 thor's general and special ideas of evolutionary sequence were set forth in a 

 series of very explicit dicta. The primitive angiosperm was indicated to have 

 been a woody, unbranched dicotyledon with simple, opposite, evergreen leaves, 

 and entomophilous, polymerous, bisexual flowers with perianth, androecium, and 

 gynoecium composed of an indefinite number of free, spirally arranged parts. 

 This prototype was believed to correspond to a Ranalian flower, and the Rana- 

 lian Plexus was therefore regarded as the point of divergence for the monocoty- 



