18 Plant-Breeding 



Now, it is apparent that in one or another of the genera- 

 tions which are thus acted upon by the environment, there 

 must be a beginning towards the fixing or hereditable 

 permanency of the new forms, and we might as well 

 assume that this beginning takes place in the first genera- 

 tion as in the last, since there can be no proof that it does 

 not take place in either one. The tendency towards 

 fixity, if it exists at all, undoubtedly originates at the very 

 time that the variation itself originates, and it is only 

 sophistry to assume that the form appears at one time 

 and the tendency towards permanency at another time. 

 Since plants fit themselves into their circumstances by 

 means of adaptive variations, we must conclude that all 

 adaptive variations have the power of persisting, upon 

 occasion. 



All these remarks, whilst somewhat abstruse, have a 

 most important bearing on the philosophy of the origin 

 of garden varieties, because they show, first that changes 

 in the conditions in which plants grow introduce modifi- 

 cations in the plants themselves, and second, that wher- 

 ever any modification occurs it is probable that it may 

 be fixed and perpetuated. 



Natal and post-natal variations. It is necessary at this 

 point that we distinguish between natal and post-natal 

 variations, that is, between those variations which are 

 born with plants, and those which appear, as a result of 

 environment, after the plant has begun to grow. It is 

 commonly assumed that the form and general characters 

 of the plant are already determined in the seed, but a 

 moment's reflection will show that this is far from the 

 truth. One may sow a hundred selected peas, for example, 



