374 SCIENCE PROGRESS. 



descent, for similar simple, and presumably primitive 

 sporangial types. With the acceptance of the Eusporangiate 

 Ferns as the more primitive, this tendency disappears ; 

 the large majority of Vascular plants are Eusporangiate ; 

 there is therefore no reason to attempt to refer them to any 

 one Leptosporangiate ancestral form. We are prepared on 

 reasonable grounds to recognise a veritable brush of lines 

 of descent. Thus there is no need to look upon Isoetes 

 as necessarily a Fern or a Lycopod ; why should it not be 

 a relic of an independent series not immediately to be 

 ranked with either ? The Ophioglossaceat are not neces- 

 sarily Ferns ; is it not possible that they also may be the 

 result of an independent evolutionary line ? 



A weak point in much of the discussion of Pteridophyta 

 in the last quarter of a century has been the free resort to 

 hypotheses of "reduction," or "fusion' of parts. The 

 climax of this mode of explanation was perhaps arrived at 

 in the paper above quoted [Bot. Zeit., 1873), in which it is 

 suggested that in the Ophioglossaceae there has been "a 

 contraction of the sori with reduction of the sporangia," in 

 Lycopodium and Selaginella a " contraction of the whole 

 fertile leaf segment of the Ophioglossaceae to one sporocyst," 

 and in Psilotum a '' contraction of the whole Lycopodium 

 strobilus to three sporocysts with reduction of the sterile 

 leaf segment ". I quote these as examples of the lengths 

 to which hypotheses of reduction may go, not assuming 

 that their author would uphold them in the present position 

 of the science. In the game of whist the general maxim is 

 sometimes formulated, " When in doubt play trumps ; " and 

 so in morphology one may almost recognise as the practice, 

 " When in difficulties suggest reduction ". But the strong 

 whist player will only use his trumps with a definite object, 

 and the morphologist should only suggest reduction when 

 there is some reasonable physiological backing for such a 

 suggestion. Hitherto this principle has not been sufficiently 

 observed. 



In the Leptosporangiate forms the spore-production is 

 not complicated by the more direct influence of sexuality, 

 nor by any marked need for storage of nutrition. The 



