40 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Sand Flats and Sand Spits. — ^Not long ago the salt lake, Wal- 
lace Lake, was sheltered by rows of dunes on hoth its north and its 
south shores, but now from most of the south side the dunes have been 
swept away, and between the southern shore of Wallace Lake and the 
South lieach of the Island, there is nothing but a great sand flat over 
which the waves break during all heavy storms. Sand spits and dry 
bars quite similar in character extend out for some distance from 
either end of the island. On all of these the Arcnaria thrives, and 
here also it is despoiled by the ponies, so much so that it is almost im- 
possible to find fruiting specimens. The bareness of these stretches 
is also broken by occasional mats of LimoseUa snhulaia Ives. 
Wallace Lake and the Brackish Ponds. — Wallace Lake, though 
often for short periods shut off from the sea, is quite as salt as is the 
sea itself. In the lake is an abundant growth of Zostcra marina L., 
which is not met with elsewhere. 
Especially at the eastern end of Wallace Lake, near Life Saving 
Station No. 3, and near the Wireless Station are series of ponds reach- 
ed by the salt water only during the heaviest fall and winter storms. 
These ponds form a perfect series from the outer ones which are quite 
l)rackish to the inner which are fresh. These brackish ponds have a 
much more abundant vegetation than does Wallace Lake. In them 
are great masses of Pondweeds, Potamogeton bupleuroides Fernald, 
P. pcdinatus L., and P. ■pvsillvs L., var. ca pit at us Benn., as well as 
Ruppia maritima L., ^•ar. longipes Hagstrom. Around the borders 
of these ponds will be found Carex Oederi Retz., var. puinUa (Coss. & 
Germain) Fernald, and great clumps of Spartina Michauxiana Hitchc, 
Aster noii-hclgii L., var. Utoreus Gray, and Scirpus acutus Muhl. 
Lake Beach. — As the tides in Wallace Lake are very small or 
none at all, and as the waves during storms cannot become large and 
destructive, the Lake Beach has an abundant vegetation on its broad 
expanse. Over great stretches it is covered with a smooth green 
carpet made up of numerous species, among which are Juncus hu- 
fonius L., var. halophilus Buchenau & Fernald, Chenopodmm ru- 
hrum L., Spergularia leiosperma (Kindb.) F. Schmidt, Ranunculus 
Cymbalaria Pursh, PotcntUla pacifica Howell, Plantago major L., var. 
inter^nedia (Gilibert) Dene., and P. decipicns Barneoud. Out of the 
sward formed by these lowly plants grow the less numerous taller ones, 
such as Ruinex man'fimvs L., var. fueginus (Phil.) Dusen, and Atrip- 
lex patida L., var. hastata (L.) Gray. 
