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 both 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 Beach 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 Arenaria 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 Limosella subulata 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 Zoster a 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 

 brackish 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 Pond weeds, Potamogeton bupleuroides Fernald, 

 P. pectinatus L., and P. pusillus L., var. capitatus Benn., as well as 

 Ruppia maritima L., var. longipes Hagstrom. Around the borders 

 of these ponds will be found Carex Oederi Retz., var. pumila (Coss. & 

 Germain) Fernald, and great clumps of Spartina Michauxiana Hitchc., 

 Aster novi-belgii L., var. litoreus 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 bu- 

 fonius L., var. halophilus Buchenau & Fernald, Chenopodium ru- 

 brum L., Spergularia leiosperma (Kindb.) F. Schmidt, Ranunculus 

 Cymbalaria Pursh, Potentilla pacifica Howell, Plantago major L., var. 

 intermedia (Gilibert) Dene., and P. decipiens Barneoud. Out of the 

 sward formed by these lowly plants grow the less numerous taller ones, 

 such as Rumex maritimus L., var. fueginus (Phil.) Duse"n, and Atrip- 

 lex patula L., var. hastata (L.) Gray. 



