Polymorphic Species 69 
Sports and spontaneous variations must now be considered. It 
is well known that they have produced a large number of fine 
horticultural varieties. The cut-leaved maple and many other trees 
and shrubs with split leaves are known to have been produced 
at a single step; this is true in the case of the single-leaf strawberry 
plant and of the laciniate variety of the greater celandine: many 
white flowers, white or yellow berries and numerous other forms 
had a similar origin. But changes such as these do not come under 
the head of adaptations, as they consist for the most part in the loss 
of some quality or organ belonging to the species from which they were 
derived. Darwin thinks it impossible to attribute to this cause the 
innumerable structures, which are so well adapted to the habits of life 
of each species. At the present time we should say that such adapta- 
tions require progressive modifications, which are additions to the 
stock of qualities already possessed by the ancestors, and cannot, 
therefore, be explained on the ground of a supposed analogy with 
sports, which are for the most part of a retrogressive nature. 
Excluding all these more or less sudden changes, there remains 
a long series of gradations of variability, but all of these are not 
assumed by Darwin to be equally fit for the production of new 
species. In the first place, he disregards all mere temporary varia- 
tions, such as size, albinism, etc.; further, he points out that very 
many species have almost certainly been produced by steps, not 
greater, and probably not very much smaller, than those separating 
closely related varieties. For varieties are only small species. Next 
comes the question of polymorphic species: their occurrence seems to 
have been a source of much doubt and difficulty in Darwin’s mind, 
although at present it forms one of the main supports of the pre- 
vailing explanation of the origin of new species. Darwin simply states 
that this kind of variability seems to be of a peculiar nature ; since 
polymorphic species are now in a stable condition their occurrence 
gives no clue as to the mode of origin of new species. Polymorphic 
species are the expression of the result of previous variability acting 
ona large scale; but they now simply consist of more or less numerous 
elementary species, which, as far as we know, do not at present exhibit 
a larger degree of variability than any other more uniform species. 
The vernal whitlow-grass (Draba verna) and the wild pansy are the 
best known examples; both have spread over almost the whole of 
Europe and are split up into hundreds of elementary forms. These 
sub-species show no signs of any extraordinary degree of variability, 
when cultivated under conditions necessary for the exclusion of inter- 
crossing. Hooker has shown, in the case of some ferns distributed 
over still wider areas, that the extinction of some of the intermediate 
forms in such groups would suffice to justify the elevation of the 
