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.' 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. 
TT 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. 
