742 



THE AMERICAN NATURALIST 



[Vol. XLH 



being alike in function, in structure, and in capacity for fission 

 and extension: the numb<r and position ar< points of difference." 



The Filicales are considered to be a phylum showing funda- 

 mentally the strobiloid characters, hut secondarily modified in 

 relation to their pronounced meg-aphyllous habit. "Accordingly, 

 the Filicales appear as the most d'nurgoit phylum of homo- 

 sporous Pt< ridophytes." 



"Comparison of tin si mat phyla, as ri pn senti d both by their 

 fossil and their modi m r< prist ntatives. It ads in iach ease towards 

 the recognition of a primitive type, find its construction in the 

 several phyla has certain features in common. The chief of 

 these are the definition of axial polarity in the first initiation of 

 the embryo: the cunt i m !•■< I ; i p i < • -• ) I m'nwth; tin- r;n I i;i 1 construction 

 of the shoot: the origin of the appendages laterally from the 

 axis by enation, and in strictly acropetal order: a protostelic 

 structure of the conducting system of the axis, and a leaf-trace 

 composed of a single strand." 



"The sporophyte . . . probably arose originally as a structure 

 of limited size, and unbranched, upon a prothallus of consider- 

 able dimensions, and producing llomnsporous Spores." 



"The adoption of Heterospory, and of the Seed Habit super- 

 vened later. This, while it has led to the final independence of 

 the land flora as regards external fluid water for the completion 

 of its life-cycle, has brought as a secondary consequence a wide- 

 spread reduction." 



"The final goal of all organic development is the establishment 

 of new individuals. The evolutionary story of the sporophyte 

 illustrates this in two distinct ways. In the prior and non- 

 spuializid Immosporous forms largi uumbirs of germs are pro- 

 duced: . . . consequently amplification of thi whole sporophyte 

 is the leading characteristic of thest earlier types; . . . In the 

 later and mon specialized heterosporous forms and particularly 

 in the Seed Plants with their mon refined methods, individual 

 precision supersedes men numbers; and reduction of the propa- 



I >.t., i. ItoroHTox Campbell. 



