Cleavers. 129 



have little wings or filaments, as in the case of the 

 dandelion or the valerian ; ani these get blown by 

 thc wind to their final resting-place. Yet others, 

 again, are provided with hooks or prickles, like the 

 burr and the houndstongue, by whose means they 

 cling to the v.-ool of sheep, the feathers and legs of 

 birds, or the hair of animals, and thus get carried from 

 hedge to hedge and rubbed off against the bushes, 

 so as to fall on to the ground beneath. Now this 

 last plan is especially well adapted for a plant like 

 the goose-grass, which lives by straggling over low 

 brambles and hawthorns, for it ensures the deposition 

 of the seed in the exact place where the full-grown weed 

 will find such support and friendly assistance as it pecu- 

 liarly requires. Accordingly, we may be sure that if 

 any half-developed goose-grass ever showed any 

 tendency to prickliness on its fruit, it would gain a 

 great advantage over its neighbours in the struggle 

 for existence, and the tendency would soon harden 

 under the influence of natural selection into a fixed 

 habit of the species. Is there any way in which such 

 a tendency could be set up .-' 



Yes, easily enough, as it seems to me. You 

 remember the outer coat of the fruit is really the 

 calyx, and this calyx would be naturally more or less 

 hairy, like the original leaves. We have only to sup- 



