348 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



term Coniferae. Berry held that the conifers comprised three main groups, viz., 

 Coniferales, Araucariales, and Taxales, all ranking equally with the Ginkgoales 

 and Cordaitales. Van Tieghem and Costantin subdivided the Vectrices into the 

 orders Taxineae, Cupressineae, and Abietineae, but these do not correspond to 

 Berry's units. Two orders were more frequently discerned in the Coniferae, 

 and usually named Taxoideae (Taxales) and Pinoideae (Finales). The divi- 

 sion of the conifers by Lotsy (1911) into Florales and Inflorescentiales (cf. 

 above) takes a special position. The remaining systems merely divided the coni- 

 fers into families. The greatest contrasts in this respect were between the system 

 of Engler and Gilg with two families, Taxaceae and Pinaceae, on the one hand, 

 and on the other, those of Pilger with seven families (Taxaceae s. str., Podo- 

 carpaceae, Araucariaceae, Cephalotaxaceae, Pinaceae s. str., Taxodiaceae, and 

 Cupressaceae) and Seward's (1919) with nine (Araucarineae, Cupressineae, 

 Callitrineae, Sequoiineae, Sciadopitineae, Abietineae, Podocarpineae, Phyllocla- 

 dineae, and Taxineae). Most students still referred the three genera of the Gne- 

 tales to one family only — Gnetaceae — but Markgraf (1926) subdivided them into 

 three families, one for each genus, and Van Tieghem and Costantin into two 

 orders, viz., the Ephedrineae, comprising the Tumboaceae {Weliuitschia) and 

 Ephedraceae, and the Gnetineae, with the Gnetaceae. 



The Modern Period (from 1930) 



While the rise of genetics has tended to draw attention from taxonomy and 

 to reduce its prestige, recent developments indicate a trend towards a synthesis 

 of the phylogenetical and the causal approaches to evolutionary problems (Mayr, 

 1949; and others). The mechanism of the evolution of the higher categories was 

 regarded by Stebbins (1950) as a continuation of the processes giving rise to 

 subspecies and species, and the origin of the former as largely a matter of time, 

 and of further genetic and environmental changes. 



Gaussen (1944-1952; cf. Ferre, 1952) formulated the following "evolutionary 

 laws" : 



1. The most recent species of a phylum are generally more evolved in all characters 

 than their ancestors. 



2. When a character evolves in a definite direction, this is always maintained, and 

 there is never a return to a more primitive type (seemingly, a return to an ancestral type 

 may ensue on overevolution). 



3. In a phylum the species generally increase in size in the course of evolution (al- 

 though overevolution may lead to an apparent return to ancestral conditions). 



4. Evolution proceeds towards specialization of organs and decrease in their number, 

 as well as towards reduction in the size of certain of them, which tend to disappear; when 

 organs have become simple, they may fuse into a complicated structure, which is then in 

 its turn simplified. 



5. The great plant groups replace one another in the course of geological times, each 

 having a juvenile or primitive phase, a mature or evolved phase, and an old or over- 

 evolved phase. 



In respect to evolutional juvenility, Gaussen distinguished three cases (cf. 

 Ferre, 1952), 



1. When a species is at the beginning of the evolution of the phylum, its juvenile forms 

 indicate the future evolutionary trend in that phylum; the juvenile form is evolved, the 

 adult primitive. 



