MEANS OF DISPERSAL. 53 



closely to any object they may touch. The plants 

 found in ponds of extreme isolation, according to this 

 observer, are not usually species with succulent fruits, 

 such as are known to be habitually eaten by birds, 

 and species with burrs or hooked fruits are by no means 

 abundant ; most of them, in fact, have the fruits dry- 

 seeded and thin shelled, which, if eaten at all, would 

 probably be digested and have their vitality destroyed ; 

 even water- thy me {Elodea canadensis), which is fruitless 

 in this country, sometimes occurs in isolated dew-ponds. 

 It seems probable, therefore, that most of these plants 

 are " transported in fragments, which breaking, cling to 

 the feet of waders, to be washed off when the bird flies 

 to the next pond," and this, it is added, " will also 

 account for the constant occurrence of the Limnseids, 

 which both adhere to the stems and attach their eggs 

 to them." Large numbers of young or small molluscs 

 might be transported together in this way. On one 

 occasion, on examining a small quantity of horned pond- 

 weed [Zannickellia), which had been taken home (after 

 having been well shaken to get rid of snails) from an 

 isolated pond on the South Downs, Mr. Reid found, 

 adhering to it, fully 150 specimens of Livtncea and 

 Planorbis, mostly very minute, and several clusters of 

 eggs ! Some molluscs, it is true, live much in or on the 

 mud, and do not attach their eggs to plants, or are 

 viviparous, but most of these, I believe, at some period 

 of their existence, or during certain parts of the year, 

 are to be met with among the leaves and stems of the 

 water-weeds. 



