632 GENERAL COMPARISON OF THE FILICALES 



that that type was probably the tropho-sporophyll ; in fact, the Ferns show 

 a Selago condition of their shoot. 



As in other Pteridophytes, so here the question is an interesting one 

 at what period fertility of the plant may begin. In most Ferns the period 

 is late, especially in the larger forms, and, as in the strobiloid types, this 

 may be ascribed to a progressive sterilisation of the earlier leaves. But in 

 other cases the formation of sori may happen relatively early, and these 

 serve to direct attention to what was probably a more primitive condition. 

 As examples where an early fertility is seen there may be quoted Blechinun 

 lanceolata, Swartz, in which, however, no exact record was kept of the leaf 

 on which sporangia were first seen. In specimens of Pteris heteropliylla, 

 L. var. internata, supplied by Messrs. Hill, the fourth or fifth leaf of the 

 seedling already produced sori ; but an extreme case is that quoted by 

 Prantl, 1 of Lygodium subalatum, in which not only are the normal leaves 

 fertile to the base, but it was noted also that the sub-primordial leaves, 

 and even the primordial leaves bear "sorophores," so that completely 

 sterile leaves are hitherto quite unknown in this species. Such an example 

 points clearly to the conclusion that in Ferns, as in other Pteridophytes, 

 all the leaves of the sporophyte are potential sporophylls. 



A minor character too little used in comparison as yet is to be found 

 in the superficial appendages. These may be filamentous or scale-like : 

 the latter are readily recognised by their development as flattened expansions 

 of the former. Speaking generally, the hair is characteristic of relatively 

 primitive types, such as the Botryopterideae, Hymenophyllaceae, and 

 Osmundaceae, while the scale or ramentum is found very generally among 

 the Leptosporangiate Ferns, though it is also present in some of the Gradatae 

 and Simplices. It is to be noted that in a considerable number of cases 

 ramenta accompany a dictyostelic structure, though there is no constant 

 coupling of the two characters. A good example of their phyletic signifi- 

 cance is to be found in the Schizaeaceae, in all of which, excepting Mohria, 

 the appendages are of the primitive filamentous type ; but in Mohria^ 

 which is regarded on various other grounds as a relatively advanced genus, 

 and has a dictyostelic stock, the appendages are flattened scales. It is 

 possible that such characters may never acquire the systematic importance 

 claimed for them by Kiihn, 2 but they certainly must not be overlooked as 

 evidence having some degree of phyletic value. 



SPORE-PRODUCING MEMBERS. 



The sporangia of Ferns are usually grouped in sori ; but apparent 

 examples occur even among the most primitive types, as well as among 

 those which are more recent, of their non-soral disposition. The first 

 question will therefore be, what was the mode of disposition of the 

 sporangia in the first instance ? 



1 Schizaeaceen, p. 14. a Prantl, I.e. , p. 13. 



