MR. C. REID OX TI1E NATURAL HISTORY OF ISOLATED PONDS. 283 
appearance around new ponds. 1 believe that Carex jmlicaris , 
C. panindata, C. vulpina, C. glauca, Juncus communis, and 
J bufonius are all common ; and P hr ag mites is certainly abundant 
where safe from treading down, and where there is a sufficient 
depth of soft soil at the bottom of the pond. 
A few of the clear-water ponds in old quarries and gravel-pits 
are full of Cham fragilis ; I have not noticed any other species of 
the genus under such circumstances, and even Chara frag His 
is rare. 
Those plants which arc of most common occurrence in dew-ponds 
are the floating species, with finely divided leaves, and with fruit 
ripening in or on the water. The comparative rarity of erect 
aquatic forms may be principally due, however, to the prevention 
of fruiting, through the treading down of the plants by animals 
that come to drink at the pond. That this is the cause, to a large 
extent, of the poverty and peculiarity of the flora of the dew-ponds, 
is shown by the fact that upright plants, such as Bulrushes and 
Burr- reeds, occur abundantly in pools inaccessible to large mammals. 
Thus it seems probable that many more species are brought to each 
dew-pond than can establish themselves under such unfavourable 
conditions. But even under circumstances not favourable for the 
introduction of new forms — except that for the first comers there 
is no competition with other plants — we learn that a considerable 
proportion of our aquatic flora can find its way into recently-formed 
isolated ponds, and must, therefore, have greater facilities for 
transport than is often imagined. 
The question next arises, how do the plants and animals, found 
thus isolated, succeed in crossing the intervening deserts and 
reaching the small oases formed by distant ponds in the middle of 
a dry country ? Wo have singularly little direct evidence as to the 
mode of dispersal in the groups with which we are now r dealing. 
The plants are not species with succulent fruit, such as we know' 
are habitually eaten by birds ; and species with burrs or hooked 
fruit are by no means abundant among them. The list is essentially 
a list of plants with fruit dry-seeded and thin-shelled, which, if 
eaten at all, would probably be digested and would have their 
vitality destroyed. Sparganiuni and Potamogeton alone have 
a somewhat succulent outer coat, surrounding a hard woody seed, 
which might pass through the digestive canal of a bird uninjured. 
