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SCIENCE 



[N. S., Vol. XL,, Ko. 1028 



structure preserved had been detected from 

 the primary rocks, showing this interme- 

 diate condition between the homosporous 

 type and that of the Pteridosperms. This 

 unsatisfactory position has now been re- 

 solved by Professor Lignier, who has re- 

 cently described, under the name of Mit- 

 tagia, a fossil from the Lower Westphalian, 

 which bore sori of which the sporangia con- 

 tained four megaspores, while the outer 

 tissues of the sporangia resembled those of 

 Lagenostoma. Pending the discovery of 

 further specimens, these observations may 

 be welcomed as filling with all probability 

 a conspicuous gap in the evolutionary se- 

 quence of known forms. 



From the rapid survey which I have been 

 able to give you of some of the more notable 

 Australasian ferns of relatively archaic 

 type, it is clear that they have a very inter- 

 esting and direct bearing upon the phylesis 

 of ferns. The basis upon which conclusions 

 as to phyletic sequence are arrived at is at 

 root that of the natural system of classifica- 

 tion generally — the recognition not of one 

 character, or of two, but of as many as pos- 

 sible, which shall collectively serve as cri- 

 teria of comparison. In the case of the 

 Filicales we may use the characters of: — 

 (i) External form, 

 (ii) Constitution, as shown by simple 



or complex segmentation, 

 (iii) Dermal appendages, hairs or scales, 

 (iv) Stellar structure, simple or com- 

 plex. 

 (v) Leaf-trace, coherent or divided, 

 (vi) Soral position, 

 (vii) Soral construction, 

 (viii) Indusial protections, 

 (ix) Sporangial structure and mechan- 

 ism of dehiscence, 

 (x) Spore-output. 



(xi) Spore-form and character of wall, 

 (xii) Form of prothallus. 



(xiii) Position of the sexual organs, 

 sunken or superficial. 



(xiv) Number of spermatocytes and 



and method of dehiscence, 

 (xv) Embryology. 

 In respect of all these criteria progressions 

 of character may be traced as illustrated 

 by known ferns, and probably other cri- 

 teria may emerge as study progresses. In 

 each case, upon a footing of general com- 

 parison, checked as opportunity offers by 

 reference to the stratigraphical sequence of 

 the fossils, it may be possible to distinguish 

 with some degree of certainty what is rela- 

 tively primitive from what is relatively 

 advanced. Thus, the protostele is gen- 

 erally admitted to be more primitive than 

 the dictyostele, the simple hair than the 

 flattened scale, and a high spore-output 

 than a low one. 



Applying the conclusions thus arrived at 

 in respect to the several criteria, it becomes 

 possible upon the sum of them to lay out 

 the species and genera of ferns themselves 

 in series, from the primitive to the ad- 

 vanced. In proportion as the progressions 

 on the basis of the several criteria run 

 parallel, we derive increased assurance of 

 the rectitude of the phyletic sequences thus 

 traced, which may finally be clinched, as 

 opportunity offers, by reference to the 

 stratigraphical occurrence of the corre- 

 sponding fossils. This is in brief the 

 phyletic method, as it may be applied to 

 ferns. It may with suitable variation be 

 applied to any large group of organisms, 

 though it is seldom that the opportunities 

 for such observation and argument are in 

 any sense commensurate with the require- 

 ments. Perhaps there is no group of 

 plants in which the opportunities are at 

 the moment so great as in the Filicales, and 

 they are yielding highly probable results 

 from its application. 



The greatest obstacle to success is found 



