PHYLOGENY 437 



cells in the microspore is more extensive in the Araucariaceae, es- 

 pecially in Araucaria, than in any other known seed plant. There 

 are often twenty or thirty prothallial cells, and as many as forty 

 have been counted. Even the highest numbers recorded for any of 

 the Abietaceae are insignificant in comparison. There is no doubt 

 that the original gametophytes were green and independent. The 

 retention of the gametophytes and their progressive reduction is 

 well known. Pinus has only two evanescent prothallial cells, and 

 the Cupressaceae, none at all. In this feature the Araucariaceae are 

 the most primitive of living conifers. Not much is known about the 

 male gametophyte of Cordaitales, but the best-preserved material 

 indicates that there were many prothalHal cells. 



As far as the evidence from the female gametophyte is known, it 

 is similar, except that in the Abietaceae there is a distinct ventral 

 canal cell, while in the Araucariaceae no wall is formed between the 

 ventral canal nucleus and that of the egg. 



In the conifers a reduction in the number of free nuclei in the early 

 embryogeny seems to be an evolutionary tendency. The Araucaria- 

 ceae have thirty-two or sixty-four free nuclei, while in the Abietaceae 

 the prevalent number is only four. In this feature the Araucariaceae 

 are more primitive than the Abietaceae. 



On the whole, it is certain that in gametophytic structures and in 

 early embryogeny the Araucariaceae are more primitive than the 

 Abietaceae, while, on the other hand, the anatomy of the sporophyte 

 would indicate that the Abietaceae are more primitive. 



If the geological record were complete, the comparative antiquity 

 of Pinus and Araucaria and the rest would be settled definitely, al- 

 though there would still remain the problem of determining whether 

 their similarity was due to parallel development from a common 

 ancestor, or to genetic continuity. 



Zeiller and Fliche^'^- '^^ found pine cones of both the Strobus 

 and Pinaster types already differentiated in the Jurassic of France; 

 and Nathorst^" concluded, on the evidence of winged pollen grains, 

 that pines existed in the Triassic of Sweden. This would bring 

 the Abietaceae into connection with the Cordaitales. 



The Araucariaceae are also very ancient, and were believed to 

 have been abundant in the Carboniferous, on account of the Aran- 



