176 NATURAL SCIENCE [September 



in adaptation to the aerial medium. Numerous other illustrations 

 could be given. 1 



I think it must be from not being aware of the abundance of 

 evidence of this sort, that the idea arose that all the offspring did 

 not acquire the same characters when the external conditions were 

 changed. 



Dr Wallace doubts it because, he says, " the argument is, that 

 the same causes will always produce the same or closely similar 

 results. But this is only true when the same causes act upon 

 identical materials and under identical conditions." 2 Dr 

 Wallace is mistaken in supposing that nature pays any attention 

 to " individual differences " which occur between any number of 

 plants of the same kind. It is not a question of argument, but 

 of facts. These differences are of no moment whatever when 

 self-adaptation is required to take place. The external influences 

 cause all the individuals to change alike in the same direction, and 

 utterly ignore the various dimensions among the " individual differ- 

 ences " described above. The result is that the same facies is ac- 

 quired by all the individuals, though a new set of individual differences 

 may readily be found among the individuals of the new variety. 



Secondly, besides doubting the occurrence of the same definite 

 variations in the whole of the offspring subjected to new but 

 similar external conditions, Dr Wallace adds : — " It must do more 

 than this, for it must produce a variation so exceptionally stable 

 that it constantly recurs in all the offspring of successive genera- 

 tions, even though those offsprings are subjected to considerable 

 change of conditions." 3 



But the stability of a species, I repeat, is a purely relative 

 matter and depends upon time. Some plants are very plastic, 

 others are not so, some variations may become very (but never 

 absolutely) rigidly fixed, while others may refuse to be reproduced 

 by seed with any certainty at all. Not only is this true when the 

 plant is propagated by seed but it is also true for vegetative multi- 

 plication. Tulips, &c, introduced from the East, though they have 

 presumably been constant in form for unknown ages, yet often 

 become unrecognisable in three years though propagated by bulbils 

 only ; apple trees, though propagated by grafts alone have given rise 

 to numerous varieties ; even different kinds of apples raised on 

 stocks, but grown in the same States of N. America, respectively, 

 often bear fruit of approximately the same form. 4 On the other 

 hand the Jerusalem artichoke, asparagus, sea-kale and celery oiler 



1 The reader is again referred to " The Origin of Plant Structures'' for further 

 details. 



'-' Loc. cit., p. 488. :! hoc. cit., p. 489. 



4 "Hud Variation and Evolution," Natural Science, vol. vii., p. 103. An essay in 

 Mr Bailey's work "The Survival of the Unlike," 1896. 



