306 DARWINISM chap. 



by floating in rivers and lakes, and thus reaching other locali- 

 ties. During the elevation of land areas this method would 

 be very effective, as the new land would always be at a lower 

 level than that already covered with vegetation, and therefore 

 in the best position for being stocked with plants from it. 



The other modes of dispersal of seeds are so clearly adapted 

 to their special wants, that we feel sure they must have been 

 acquired by the process of variation and natural selection. 

 The hooked and sticky seeds are always those of such her- 

 baceous plants as are likely, from their size, to come in 

 contact with the wool of sheep or the hair of cattle ; while 

 seeds of this kind never occur on forest trees, on aquatic 

 plants, or even on very dwarf creepers or trailers. The 

 winged seed-vessels or seeds, on the other hand, mostly belong 

 to trees and to tall shrubs or climbers. We have, therefore, a 

 very exact adaptation to conditions in these different modes of 

 dispersal ; while, when we come to consider individual cases, 

 we find innumerable other adaptations, some of which the 

 reader will find described in the little work by Sir John 

 Lubbock already referred to. 



Edible or Attractive Fruits. 



It is, however, when we come to true fruits (in a popular 

 sense) that we find varied colours evidently intended to 

 attract animals, in order that the fruits may be eaten, while 

 the seeds pass through the body undigested and are then in 

 the fittest state for germination. This end has been gained in 

 a great variety of ways, and with so many corresponding 

 adaptations as to leave no doubt as to the value of the result. 

 Fruits are pulpy or juicy, and usually sweet, and form the 

 favourite food of innumerable birds and some mammals. They 

 are always coloured so as to contrast with the foliage or 

 surroundings, red being the most common as it is certainly the 

 most conspicuous colour, but yellow, purple, black, or white 

 being not uncommon. The edible portion of fruits is developed 

 from different parts of the floral envelopes, or of the ovary, in 

 the various orders and genera. Sometimes the calyx becomes 

 enlarged and fleshy, as in the apple and pear tribe; more 

 often the integuments of the ovary itself are enlarged, as in 

 the plum, peach, grape, etc. ; the receptacle is enlarged and 



