242 AMPLIFICATION AND REDUCTION 



end in itself, b'ut only a means to the end, viz., the suitable nutrition 

 of the nascent germs. There are several ways in which this nutrition 

 may be effected ; they are these : 



(1) Nutrition by the gametophyte, which was the most primitive 



method. 



(2) Self-nutrition of the sporophyte by its own assimilatory system. 



(3) Indirect nutrition of the sporophyte, e.g. by mycorhiza. 



Provided the spore-production be maintained, it matters not which of 

 these is effective, or dominant in any individual case ; and in point of 

 fact they have varied in the phyletic history. In the original state of the 

 sporophyte there was undoubtedly nutrition by the first method. Subse- 

 quently the second supervened ; and there is reason to think that during 

 the phyletic history there has been a varying balance of the effectiveness 

 of these two factors. Generally speaking (i) has waned in importance 

 proportionately to the whole requirement ; but in such cases as the 

 Moss-sporogonia with non-functional stomata, and in the large under- 

 ground prothalli of Lycopods and Ophioglossaceae (i) appears again to 

 have increased in proportional importance, encroaching upon the effective- 

 ness of (2), with the result that local reduction of the mechanism of 

 self-nutrition in the sporophyte followed ; but still that may have pro- 

 duced no ill effect upon the spore-output. Passing to the independent 

 sporophyte, its primitive nutrition was autotrophic (2), and there was a 

 suitable balance of the nutritive and propagative systems, the method of 

 which differed in the different phyla. Lastly, in those cases where 

 indirect nutrition (3) by mycorhiza contributes effectively, a reduction of 

 the normal nutritive system of the sporophyte may take place ; but so 

 long as the sum of nutrition is maintained the propagative system would 

 not be reduced. If, however, for any reason the sum of nutrition fall, 

 then general reduction would ensue. 



It is not then enough to suggest reduction on mere grounds of com- 

 parative convenience : to make the suggestion convincing in any group 

 where general reduction is believed to have occurred, it will be necessary 

 to prove that the sum of nutrition, from whatever source, has diminished 

 in the course of descent, and that reduced spore-output has been the 

 result. Until this has shown to have occurred in any case, there seems 

 no sufficient reason to accept as more than a quite open hypothesis any 

 suggestion of general reduction of its sporophyte. The biological probability 

 is against extensive, or general, reduction in homosporous forms, and in 

 any case the positive balance during the whole phyletic history must 

 have been on the side of amplification. 



But where there is heterospory, and especially in plants showing the 

 seed-habit, where a high certainty of a germ becoming effectively established 

 is attained by storage in the enlarged spore, reduction in the number of 

 spores followed, and the cognate reduction of other parts assumed many 



