102 STERILISATION 



speculate upon such questions : for the present it is best to be content 

 to recognise as an unsolved problem what those influences are which 

 encourage or check reduction in any individual cell of a sporogenous 

 tissue at the critical moment. 



In conclusion, the question may be raised how sterilisation is to be 

 viewed : is it an advance or a retrogression ? If the antithetic theory of 

 alternation be true, then sterilisation must be regarded as an evolutionary 

 advance, as far as it influences the whole organism. According to our theory, 

 it is by successive stages of sterilisation, following closely upon the heels 

 of increase of potential sporogenous tissue, that the vegetative body of the 

 sporophyte originated, and enlarged. A new phase of life of increasing 

 importance was thus intercalated, the end and result of which was primarily 

 an increased spore-output. But its origin was, conversely, in restricted 

 propagative development of certain cells. Inasmuch as this has tended 

 to a higher state, and greater success of the whole organism, it may be 

 held to have been an advance. But as regards the individual cell, 

 sterilisation can only be held to be a check to its development, as it 

 prevents it from taking direct part in the final end of the sporophyte, 

 which is the production of new germs. 



From the examples quoted there is ample proof that sterilisation of 

 .potentially fertile cells does occur : thus from living plants the evidence 

 is supplied of the existence of that factor which is the first essential of 

 any theory of origin of the sporophyte by expansion from the zygote. It 

 does not necessarily follow that the first vegetative tissues of the sporophyte 

 did originate in this way : all that can be claimed is that plants show 

 not uncommonly to-day such a conversion of cells from the propagative 

 .to the vegetative state as the antithetic theory would demand. 



