THE BIOLOGICAL CRITERION 243 



different forms. These need nob be detailed here : it will suffice to quote 

 as one example of a case fully made out the reduction of the sporophyll 

 in the Cycadales. 



It is thus seen that hypotheses of relative primitiveness, or of reduction 

 as applied to living organisms, do not stand on an equal footing. The 

 former has the logically prior claim, and should be accepted as a 

 working theory until good grounds can be given for preferring the latter ; 

 and the mere exigencies of comparison will not be sufficient : a proper 

 foundation can only be sought in the biological circumstances of the 

 organism in question. Such evidence is specially necessary when dealing 

 with homosporous forms, in which the problem is more directly one of 

 size, nutritive capacity, and consequent spore-number, than in the case 

 of those which are heterosporous. 1 



1 Compare Bower, Science Progress, vol. iv., p. 358, etc. Also Tansley, Neiv Phytologist, 

 vol. i., p. 131. 



