3IO MORPHOLOGY OF GYMNOSPERMS 



leads to the habit and structure of Coniferales, as the former does to 

 that of Cycadales. The habit of the body, the thick vascular cylinder, 

 the entire leaves, the structure of the ovulate strobilus, are all con- 

 spicuous features of Cordaitales that are carried forward by the Conif- 

 erales, and are in strong contrast with the features of the cycadophytes. 

 Apparently the most important change observed in the Coniferales is 

 the abandonment of the swimming sperm with its associated pollen 

 chamber. It must be remembered, however, that the record of this 

 change is obtained by contrasting living conifers with paleozoic 

 Cordaitales, and that there is really no evidence as to when it occurred 

 or in what group. 



There are two views as to the origin of Pinaceae which differ from 

 the one expressed above, and which deserve mention. 



In his investigation of the secondary wood of Coniferales, Pen- 

 hallow (96, 133) has reached the conclusion that the Pinaceae have 

 come from the Taxaceae (that is, a primitive taxad stock), which in 

 turn are a phylogenetic branch from the Cordaitales. So far as the 

 Cordaitean origin of conifers is concerned, this view agrees with the 

 preceding one; but as to the primitive conifers, the two views are 

 directly contradictory; and the latter view seems to be contradicted 

 also by history, especially as the phylogenetic succession proposed 

 is Taxodineae, Cupressineae, and Abietineae, with Pinus as the most 

 modern genus. The conclusions are based upon the assumption that 

 greater complexity of structure necessarily indicates a more modern 

 form. It must be kept in mind, in connection with all these views, that 

 the tribes as represented in our present flora are not thought of as 

 ancestral forms, but that they represent the ends of successive branches 

 that have arisen from a common coniferous stock. This investigator 

 concludes also that the Araucarineae had an independent and direct 

 origin from the Cordaitales, which is one of the alternatives mentioned 

 above. 



The other view referred to is that of Seward (105, 117, 118), 

 who has argued for the origin of Araucarineae from Lycopodiales. 

 This is an older view (Sachs, Eichler, Potonie) that had passed 

 out of notice in connection with recent work. Seward urges that the 

 primitive character of araucarians is shown by (i) the gradual transi- 

 tion from ordinary foliage leaves to sporophylls (also often green); 



