ADAPTATIONS FOR DISPERSAL OF FRUIT & SEEDS 217 



trees and slirubs, the seed (stone) is not swallowed by 

 tbe bird. Tlie fleshy portion is sticky and the bird to get 

 rid of the seeds which adhere to its bill^ wipes them off 

 on to a branch. In this way the seed is placed in the 

 most adyantageous si)ot for germination. In many 

 frnits which ai-e not succulent the seeds are either 

 coloured or possess an appendage called an " aril '\ This 

 aril seryes as an organ of attraction to birds. 



The unintentional i'V accidental dispersal of seeds is 

 of common occurrence and about 10% of plants haye con- 

 triyances of some kind for animal distribution. The 

 seeds or, as is more usually the case the fruits, are 

 furnished with hooks, spines or are sticky. 



In Geuiu (Rosaceae) the nutlets are each furnished 

 with a hook Ayhile in Bidens pilosa there are two barbed 

 bristles with reflexed hooks which form a yery effectiye 

 apparatus for clinging to passing animals; two spines 

 are produced at the apex of the fruit of Tagetes miniita 

 which answer the 5ame purpose (PI. III. fig. 9.) In 

 Agrimonia (Rosaceae) , Xantiuum spinosum (Bur-weed), 

 Medicago spp. the fruits are coyered with spines. The 

 '^Grapple Plant'' — Harpagophytum procumhens (Peda- 

 lineae) (PI. III. fig. 11.) — has an effectiye, if cruel, method 

 for seed distribution. The fruit is coyered Ayith long 

 woody somewhat elastic spines with recuryed hooks. The 

 X)lant, which trails along the ground, has the fruits so 

 placed that an animal treading on them caiTies away 

 the fruits which cling tenaciously to the foot. In 

 attempting to get rid of the clinging fruit the animals 

 stamp it to pieces and thus the seeds escape from the fruit. 

 Pretrea Zangueharlca ( Pedalineae) (PI. III. fig. 2, 20.) 

 has a fruit flat on one side and conyex on the other. On 

 the flat surface are two erect spines and the structure of 

 the fruit is so formed that the spines lie uppermost. The 

 spines will penetrate the hoof of an animal treading on 

 them and in this way the fruits may be carried some dis- 

 tance before they become detached. The late Prof. Mac^ 



