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. 
