THE BIOLOGICAL CRITERION 243 
different forms. These need not 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 thypotheses 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 Compare Bower, Scéence Progress, vol. iv., p. 358, etc. Also Tansley, Mew Phytologist, 
vol. i, p. 131. 
