FLORIN: SYSTEMATICS OF THE GYMNOSPERMS 345 



arguments advanced in support of it included: the resemblances between tlie 

 cordaites and the araucarians in the anatomy of the stem, root, and leaf; the 

 difficulty in explaining the cones of the Pinaceae in terms of a lycopod ancestry; 

 the structure of the seed; the multiple microsporangia. The Araucariaceae were 

 regarded as the primitive basal group of conifers, or as constituting an independ- 

 ent evolutionary line. The "abietinean" theory, advanced by Jeffrey (1912) is 

 based on the brachyblast theory of the female cone, and on certain principles of 

 comparative morphology. He argued in the following way : 



1. The ancestors of Araucaria and Agathis cannot be derived from the cordaites be- 

 cause they had wood parenchyma and strongly pitted rays in their secondary wood. 

 Certain mesozoic woods with araucarian pitting, wood parenchyma, and strongly pitted 

 rays, are of araucarian affinity; their characteristic features are retained in the wood of 

 the cone axis, root, and first annual ring of vigorous branches of living Araucariaceae. 



2. The structure of the first annual ring of mesozoic Araucarioxylon stems, as well 

 as of the seedling wood in the cone axes of Agathis and Araucaria. shows that the arau- 

 carian tracheary pitting is not ancestral, but more recently acquired. 



3. Certain mesozoic conifer woods with traumatic resin canals are of araucarian 

 affinities, since their tracheids have araucarian pitting, and there are no crassulae. 

 Abietineous pitting in the rays of extinct conifers is no reliable diagnostic feature. Trau- 

 matic phenomena supply an additional argument in favor of the derivation of the Arau- 

 cariaceae from pinaceous ancestry. 



4. The Araucariaceae cannot be derived from the cordaites, since they possessed 

 primitively a number of features which never existed in the cordaitean stock. The 

 Araucarioxylon type is derived from ancestral forms possessing opposite pitting, cras- 

 sulae, strongly pitted rays, and horizontal and vertical resin canals. 



In contrast to Jeffrey's theory, Gothan (in H. Potonie and Gothan, 1921), 

 Krausel (1919), Eckhold (1922), and others, regarded the Araucariaceae as the 

 most primitive and the Pinaceae as the most advanced conifers. The appearance 

 of a transitional group, the Protopinaceae, in the Mesozoic era was combined 

 with a reduced frequency of araucarian woods and the gradual appearance of 

 pinaceous woods. The pitting of the tracheids changed concurrently with other 

 features, e.g., the form and arrangement of the cross-field pits, the occurrence of 

 vertical and horizontal resin canals, and of ray tracheids. A phylogenetic line 

 could thus be followed from the simple woods of araucarian structure, via the 

 Protopinaceae and their nearest successors, to the modern pinaceous wood of 

 complex structure. 



That opinions on the relationships of other families also differed was to some 

 extent due to these contrasting general views. The taxads, Cephalotaxus, podo- 

 carps, and their allies, were at the beginning of the century still regarded as 

 members of one family, Taxaceae, but gradually it was realized that this was a 

 diverse assemblage, which should be divided into no less than three families, 

 viz., the Podocarpaceae, Cephalotaxaceae, and Taxaceae s. str. (Pilger, 1926). 

 Sahni (1920) even excluded the genera Taxus, Torreya, and Ceplialotaxus from 

 the conifers, and proposed for them an independent phylum, Taxales, related to 

 Ginkgo, to the Cordaitales, and to the Coniferae. According to Sahni the 

 Taxales stand apart from the conifers in the general organization of their fe- 

 male shoots, and in the fact that they retain primitive seed and seedling charac- 

 ters. He did not believe that the yews represented any relatively modern group, 

 as asserted by Jeffrey. 



Numerous contributions were made to our knowledge of the conifers of past 



