28 Rhodora [FEBRUARY 
This condition has had an important influence on the process of filling 
which has been going on since the ponds were left at the retreat of 
the ice-sheet. Their original shape seems in most cases to have been 
decidedly irregular, for every pond of any size has along its shore a 
number of indentations in all stages of filling, from shallow pools with 
thickly covered shores to peat-filled swamp-holes. These are cut off 
from the rest of the pond, at least in their later stages, by a barrier 
of sandy beach, and simply represent small arms of the original pond 
which from their sheltered position have filled rapidly and been con- 
stricted off from the main body of water. The tendency is always for 
a pond to smooth off its shores, thus approaching more and more to 
a roughly circular shape, and for the large, and especially the long 
and narrow ponds to become divided up into a number of smaller 
ones, each of which centers about some particularly broad and deep 
portion of the original. 
The flora of the pond-shores is varied and, as has been said, contains 
many characteristic Cape Cod plants which from their distribution 
are worthy of note. 
The upper edge of the beach is dry sand or gravel in summer and is 
apt to be invaded by herbaceous members of the surrounding sand- 
barren flora. Here Aletris farinosa, Polygala polygama, Cassia 
nictitans, Linum virginianum, Chrysopsis falcata and many other 
common things find a congenial habitat. 
The plants of the lower parts of the beach, however, whose roots 
are in damp sand, form a distinct group, the members of which occur 
in practically no other situation. A list of the commonest and most 
characteristic beach plants, which would be found along almost every 
undrained pond of any size on Cape Cod, includes the following:— 
Lycopodium inundatum var. Bigelovii, on damp sand and also on 
peaty mud. 
Cyperus diandrus, universal and usually the first plant to gain a 
foothold on the sterile portions of the beach. 
Rynchospora glomerata. 
Xyris caroliniana. 
Polygonum Careyt. 
Hypericum virginicum and Gratiola aurea, extremely common 
everywhere and flourishing equally well on sand or mud. 
Hypericum canadense. 
Rhexia virginica. 
