RELATIONS TO ANIMATE ENVIRONMENT 107 



cases, the evolution of many plants has been very materially 

 affected, in so far as the fruit and its dispersal are concerned, by 

 the agency of birds. 



The eminent botanist Kerner carried out a series of inter- 

 esting experiments designed to test the vitality of seeds after 

 having been swallowed by birds. As a result he found that 

 birds are in this respect divisible into three groups. The first 

 group includes those which grind up even the hardest fruits and 

 seeds in their muscular gizzards by the aid of small stones and 

 grit. Amongst these some strip the fruits and seeds when 

 they first lay hold of them, and thereby condemn them to 

 destruction. Such were, he found in his experiments, the 

 Turkey, Common Fowl, Pigeon, Duck, Cross-bill, Bullfinch, 

 Goldfinch, Siskin, Serin-finch, Nutcracker and Titmouse. No 

 seed, under ordinary conditions, was found capable of germina- 

 tion in the excrement of these birds. The seeds used were 

 those of Arenaria serpyUifolia, Papaver rhccas. Sisymbrium 

 Sophia, Ribes rubuui, Ligiistrjuii vnlgare, Fragrare indica and 

 some other species. Ravens and Jackdaws form a second 

 group, wherein the stones of the drupes and hard-coated seeds 

 of the berries which they ate passed uninjured through the 

 intestine, whilst soft-coated seeds and fruits were all destroyed. 

 Kerner draws particular attention to the fact that after these 

 birds had been fed with cherries their excrements contained 

 cherry-stones 15 mm. in diameter, every one of which was 

 able to germinate. The Blackbird, Song-thrush, Rock-thrush 

 and Robin formed a third group. Of these the Blackbird 

 proved to be the least fastidious about its food. It even 

 swallowed the fruits of the yew without afterwards relieving its 

 crop of the stony seeds, and it never rejected a single fruit that 

 was mixed with its food. The Song-thrush rejected all dry 

 fruits of 5 mm. diameter or more, even when they were mixed 

 with the finely chopped meat with which the bird was fed. 

 They also avoided such strong-smelling fruits as those of the 

 yarrow. On the other hand, the aromatic fruits of umbelli- 

 ferae were eaten with great avidity. The seeds of the tobacco 

 plant, henbane and foxglove mixed with the food were not 

 rejected and caused no ill effects, neither did the berries 

 of the deadly nightshade which were greedily devoured. On 

 the other hand, however, a Song-thrush sickened after eating 



