1915] 



BESSEY — PHYLOGENETIC TAXONOMY 111 



I may quote one more sentence from the Manchester logician 

 (p. 138) : "Agreement with fact is the one sole and sufficient 

 test of a true hypothesis. ' ' 



So I come with a general hypothesis of the evolution of 

 living things, and of plants in particular. This hypothesis is 

 based upon observed facts, which are here given such a uni- 

 form interpretation as will make my general hypothesis, and 

 it is this latter that I wish to discuss to-day, making such ap- 

 plication as will enable us to arrange the flowering plants in 



accordance with it. 

 I am going to confine my discussion pretty largely to the 



plants of the highest phylum, here restricted to those that 

 bear flowers. Since the discovery of the pteridosperms, it is 

 manifestly untenable to regard all seed-bearing plants as 

 members of one phylum. In other words, the Spermatophyta 

 of the books constitute not one phylum, but several phyla. 

 Briefly, I shall exclude first of all the cycad phylum which 

 began in the Paleozoic period with the pteridosperms, and 

 has extended with many losses to the present. I shall also 

 exclude the conifer phylum, related to but not included in the 

 cycad phylum. These two phyla are commonly associated in 

 a group under the name of gymnosperms, but I have no hesi- 

 tation in keeping them as distinct phyla, the cycads lower, and 



the conifers higher. 



The remaining seed-bearing plants, whose seeds are en- 

 closed in carpels, constituting the old group of angiosperms, 

 I regard as a distinct phylum, and because the flower is the 

 dominant and characteristic structure, I designate them as 

 the Phylum Anthophyta, and they are the flowering plants 

 about which I speak to-day. 



So in clearing the way for this discussion, let me show the 

 relationship of these three phyla of higher plants by means of 

 an analytic key, as follows : 



A. Gametophyte generation larger, and longer-lived than the dependent sporo- 



phyte generation. Here are set off the liverworts and mossea. 



B. Gametophyte generation smaller and shorter-lived than the independent 



sporophyte generation. 



(a) Here we set off those plants in which both generations are mostly holo- 

 phytic and independent of one another, the megagametophyte still con- 

 taining chlorophyll, including ferns, calamites, and lycopods. 



