1903.] 



Morphology of Spore-producing Members. 



203 



the gametophyte of the Psilotacese and Sphenophyllese are not avail" 

 able in this comparison. 



It is not obvious what the meaning is of this parallelism between 

 leaf-size and characters of the sexual organs; a further difficulty 

 in its interpretation lies in the fact that for the Equiseta the parallel- 

 ism does not hold ; there " Filicinean " characters of the gametophyte 

 accompany entirely non -Filicinean characters of the sporophyte, the 

 latter showing nearer analogy to the Lycopods than to the Ferns. 

 Such cross characters are difficult to harmonise with any phylogenetic 

 theory ; on account of them, the Equisetinese are placed in an isolated 

 position, and in the same way, though with less pressing grounds, a 

 separate position should be accorded to those types which lie between 

 the extremes of Lycopods and Ferns, in proportion as the characters 

 are more or less pronounced. 



On this basis the Isoetacese would probably best take their place as 

 a sub-series of the Lycopodiales, Ligulatse ; the Psilotacese and Spheno- 

 phyllese would constitute a series of Sphenophyllales, separate from, 

 but related to, the Lycopodiales. The Ophioglossaceae would form an 

 independent series of Ophioglossales, more aloof than the latter from 

 the Lycopodiales, but not included in the Filicales. The actual con- 

 nection of these series by descent must remain open ; it is quite 

 possible that some or all of them may have originated along distinct 

 lines from a general primitive group, which may be provisionally 

 designated the Protopteridophyta ; these were probably small-leaved 

 strobiloid forms, with radial type of construction, and with the 

 sporangia disposed on some simple plan. The grouping arrived at in 

 these Memoirs may be tabulated as follows : — 



PTEEIDOPHYTA. 



I. Lycopodiales. 



(a) Eligulatse. 



Lycopodiacete. 



(b) Ligulatse. 



Selaginellacea?. 

 Lepiclodendracese 

 Sigillariacese. 

 Isoetacere. 



II. Spenophyllales. 



Psilotacea?. 

 Sphenophyllacea? . 



III. OrHIOGLOSSALES. 



Ophioglossaceae. 



