1897] ORIGIN OF SPECIES AMONG PLANTS 173 



of life are somewhat different," If so, and this statement is quite 

 in accordance with Sir J. D. Hooker's view already quoted, how 

 could the varieties have arisen in the midst of the plant type ? 

 Similarly, Darwin says that mountain breeds always differ from 

 lowland breeds ; and " a mountainous country would probably affect 

 the hind limbs from exercising them more, and possibly even the 

 form of the pelvis," &c. What is all this but the formation of new 

 varietal structures by a response to the direct or definite action of 

 the environment ? But, then, it is obvious from Darwin's remarks 

 that the mountain breeds are not supposed to have arisen among 

 the lowland forms or vice versd ; just as the submerged forms of 

 Ranunculus could not have arisen among land buttercups or vice 

 versa. Consequently Darwin could not shut his eyes to the fact 

 that " isolation is an important element in the modification of 

 species." l Again, he says : — " Migration and isolation are necessary 

 elements for the formation of new species." 2 



On the other hand, Dr Wallace says : — " Physical isolation, I 

 believe with Darwin [?], to be of comparatively little importance, 

 and to have very rarely been the chief agent in modification." 



If migration and isolation, which are only to be secured on 

 the confines of the geographical area of a species, as Sir J. D. 

 Hooker says, are so important, then it becomes obvious that the 

 centre of the parent population is not the place, as a rule, to look 

 for the origin of a new variety, but as far away from it as possible. 

 From this it follows that the less struggle for- existence 

 there be with the parent type, the better it is for the origi- 

 nation of new varieties; and it is best of all where there 

 is no struggle at all. 



Dr Wallace enquired of two experienced British botanists if 

 there " are any cases of well-marked varieties, which occupy a con- 

 siderable area to the exclusion of the parent species, and do not occupy 

 any area, or only a very small one with the type." 3 One example 

 of a Rubus was given him ; but a more important question, however, 

 as it seems to me, would be : — Is a sub-species or variety usually 

 found within the area occupied by a large number of the parent 

 type ? Take, e.g., Hicracium, a most variable genus ; of this Sir 

 J. D. Hooker writes : — " Variable as the genus is, the sequence of 

 its forms is so natural as to have been recognised by all botanists. 

 This sequence represents to a considerable extent the spread of the 

 forms in altitude and area in the British Isles." 4 Now Hicracium 

 is not a genus with gregarious species ; for though the sub-species 

 and varieties are very many, the relative quantity of each is not 

 particularly great anywhere ; and thus, so far from lending any 



1 " Origin, etc.," p. SI. 2 " Origin, etc.," p. 82. 



3 Loc. cit, p. 494. 4 ' Students' Flora," p. 232. 



