300 DISPERSAL [ch. 



and bird play some part in one another's life. In British Guiana, 

 Im Thurn^ noticed Spurwings {Parra jacand) running about 

 over the leaves of Victoria regia ; one of them had even nested on 

 a leaf. In the case oi Lawia zeylanica^ a Podostemad belonging 

 to Ceylon, Willis^ records that wading birds are often seen 

 walking over the thalli. Very numerous fruits are produced, 

 each containing a large number of seeds, whose epidermis 

 swells up and becomes mucilaginous on wetting. This mucilage, 

 when it dries, serves to fix the small seeds firmly to any object 

 with which they come in contact, and Willis points out that 

 in this way they may easily adhere to the feet of wading birds. 



When we come, however, to the question of th.& first-hand 

 evidence as to the part played by water-fowl in the dispersal 

 of aquatic plants, we find that the facts actually recorded are 

 relatively few. Our ignorance on this point was emphasized by 

 Caspary^ in 1 870, and though almost half a century has elapsed 

 since he propounded the question " W^elche Vogel verbreiten 

 die Samen von Wasserpflanzen?" very few observers have 

 stepped into the breach. It is a question which might well en- 

 gage the attention of local natural history societies, since it 

 requires the co-operation of botanists and zoologists: an investi- 

 gation conducted over a number of seasons could scarcely fail 

 to produce interesting results. 



Such direct evidence as we at present possess, relates partly 

 to the unintentional conveyance of water plants attached to a 

 bird's feet or feathers, and partly to the presence of undigested 

 seeds and fruits in the alimentary canal. With regard to the 

 Lemnaceae, WeddelH records that, when shooting in Brazil, 

 he killed a water bird called "Camichi"; its feathers were 

 soiled with greenish matter, and closer examination revealed 

 the presence of a minute Duckweed, Wolffia brasiliensis^ in full 

 flower! At a later date Darwin^ stated that, in this country, he 

 had twice observed Duckweed adhering to the backs of Ducks 



1 Im Thurn, E. F. (1883) 2 Willis, |. C. (1902). 



3 Caspary, R. (iSyo^). 4 Weddefl, H. A. (1849). 



5 Darwin, C. (1859}. 



