310 Geographical Distribution of Plants 
incident of the Glacial period a whole flora may have moved down and 
up a mountain side, while only some of its constituent species would 
be able to take advantage of means of long-distance transport. 
I have dwelt on the importance of what I may call short-distance 
dispersal as a necessary condition of plant life, because I think it 
suggests the solution of a difficulty which leads Guppy to a conclusion 
with which I am unable to agree. But the work which he has done 
taken as a whole appears to me so admirable that I do so with the 
utmost respect. He points out, as Bentham had already done, that 
long-distance dispersal is fortuitous. And being so it cannot have 
been provided for by previous adaptation. He says!: “It is not 
conceivable that an organism can be adapted to conditions outside 
its environment.” To this we must agree; but, it may be asked, do 
the general means of plant dispersal violate so obvious a principle? 
He proceeds: “The great variety of the modes of dispersal of seeds 
is in itself an indication that the dispersing agencies avail themselves 
in a hap-hazard fashion of characters and capacities that have been 
developed in other connections.” “Their utility in these respects is 
an accident in the plant’s life?” He attributes this utility to a 
“determining agency,” an influence which constantly reappears in 
various shapes in the literature of Evolution and is ultra-scientific 
in the sense that it bars the way to the search for material causes. 
He goes so far as to doubt whether fleshy fruits are an adaptation for 
the dispersal of their contained seeds*. Writing as I am from a 
hillside which is covered by hawthorn bushes sown by birds, I confess 
I can feel little doubt on the subject myself. The essential fact 
which Guppy brings out is that long-distance unlike short-distance 
dispersal is not universal and purposeful, but selective and in that 
sense accidental. But it is not difficult to see how under favouring 
conditions one must merge into the other. 
Guppy has raised one novel point which can only be briefly 
referred to but which is of extreme interest. There are grounds for 
thinking that flowers and insects have mutually reacted upon one 
another in their evolution. Guppy suggests that something of the 
same kind may be true of birds. I must content myself with the 
quotation of a single sentence. “With the secular drying of the 
globe and the consequent differentiation of climate is to be connected 
the suspension to a great extent of the agency of birds as plant 
dispersers in later ages, not only in the Pacific Islands but all over 
the tropics. The changes of climate, birds and plants have gone on 
together, the range of the bird being controlled by the climate, and 
the distribution of the plant being largely dependent on the bird®.” 
1 Guppy, op. cit. 11. p. 99. 2 Loe. cit. p. 102. 3 Loe, cit. p. 100. 
* Loc. cit. p. 102. 5 Loc. cit. wu. p. 221. 
