I INTRODUCTION ii 



Waltheria, Kleinhovia, Sterculia, and Heritiera, that he so often 

 meets with in the Pacific Islands, have in these respects frequently 

 very little in common ; and yet one of the earliest determining 

 influences in plant-life must have lain in the capacity for dispersal. 



Yet chance seems to reign in the processes of plant-dispersal 

 ever going on around us. In the floating seed, in the achene with 

 its light pappus blown before the gale, in the prickly mericarp 

 entangled in the plumage of a bird, in the " stone " of the drupe 

 disgorged or ejected by the pigeon, in the small grain that becomes 

 adhesive in the rain, in the tiny rush-seed enclosed in the dried 

 pond-mud on the legs of some migratory bird, in all these we see 

 the agencies of dispersal making use of qualities and of structures 

 that were developed in quite another connection and for quite 

 another purpose. That such characters have been so to speak 

 appropriated by these agencies is a pure accident in a plant's life- 

 history. If the evolutionary force had been in operation here, it 

 would have selected some common ground to work on. There 

 would have been some uniformity in its methods, whereas the 

 modes of dispersal are infinite. The qualities and characters that 

 happen to be connected with dispersal belong to a plant's develop- 

 ment in a particular environment. They can never have been 

 adapted to another set of conditions that lie quite outside that 

 environment. There is a relation of a kind between the specific 

 weight of wood and the density of water, and this, in a sense, sums 

 up the connection between a seed and its distributing agencies. 



Evolution has never concerned itself directly with means of 

 dispersal. Evolution and Adaptation represent the dual forces 

 that rule the organic world, the first an intruding force, the last a 

 passive power representing the laws governing the inorganic world. 

 To these laws the intruding power has often been compelled to 

 bend, and it has had to pay its price, and sometimes it has 

 succumbed, and sometimes it has turned its defeat into a victory. 

 Nature, so watchful over the young plant, as represented by the 

 seed, is finally compelled to let it go, and dispersal begins where 

 evolution ends, or rather when the evolutionary power fails. The 

 seed-stage itself is the price of adaptation. The death of the 

 individual may also be regarded from the same standpoint. It 

 represents a defeat of the evolutionary force, which, however, has 

 been retrieved by the gift of reproductive power. 



