708 CONCLUSION 



in various ways, though probably from somewhat similar beginnings, the 

 various primitive homosporous phyla may be held to have worked out 

 the line of biological advantage which follows on direct increase of numerical 

 output of spores. This may be regarded as the upward limb of a curve 

 of morphological complexity. 



But with heterospory and especially with the Seed-Habit and more 

 precise methods of fertilisation following on siphonogamy, the line of 

 biological advantage was diverted from mere numerical increase of germs 

 to their individual nurture, with, as a consequence, a higher degree of 

 certainty of their final establishment in life. This brought in various 

 ways reduction as against the previous amplification. The most conclusive 

 evidence of this is to be found in the sequence from the Ferns, and 

 Fern-like Pteridosperms, through the Cycads. It seems impossible to see in 

 these any other story than one of simplification of appendages following 

 on increased precision of propagative method ; it may be represented as 

 the downward limb of a curve of morphological complexity. It is not at 

 present possible to indicate any other phyletic lines with the same degree 

 of certainty as this ; but the condition of the floral construction in other 

 Gymnosperms, and in the Angiosperms themselves is certainly such as to 

 harmonise with an origin in which reduction has played a prominent 

 part. 1 The biological probability that such an homosporous amplification 

 should be succeeded by a reduction following on the adoption of a Seed- 

 Habit is in full accord with the evolutionary course which the facts 

 themselves appear to indicate. 



1 I leave entirely open the question of phyletic origin of certain Gymnosperms from 

 the Lycopodiales. If that were their true origin the reduction would in that case be in 

 restriction of the number of sporophylls and sporangia rather than in size of the 

 sporophylls themselves : in fact a reversal of their homosporous amplification, analogous 

 to but not coincident with that of the larger-leaved Filicales, Pteridosperms, and Cycads. 



