TYPICAL SWAMP AREAS. 45 
winds and the coincident cooling of the earth. Johannsen * 
holds that these structural conditions are called forth by 
the reduced absorptive ability of the roots on account of 
an insufficient oxygen supply. Warming t adds to the 
above his belief that the xerophytic structure was re- 
quired because the stomata had lost the power to close 
themselves. H. Nillsont{ has arrived at the definite con- 
clusion that the xerophytic structure stands in intimate 
connection with the paucity of nourishment in the soil. 
The zonal distribution of plants is well illustrated in 
these tamarack swamps. Within the surrounding forest 
of maple, beech and hemlock, the real swamp area is 
found. The surface of the peaty soil is covered with 
Sphagnum and this zone is dominated by Larix Ameri- 
cana and Picea nigra. 
Thuya occidentalis is next in importance and Acer 
rubrum, Betula lutea and Pyrus Americana are among the 
most noticeable of the remaining trees, though they are 
only occasionally found. Beginning in this zone and ex- 
tending to the water’s edge is an immense tangle of waist 
high shrubbery in which the leather leaf is most pre- 
dominant, closely followed by Kalmia glauca, Vaccinium 
Canadense, Gaylussacia resinosa, Ilex verticillata, Nemo- 
panthes fascicularis and Pyrus arbutifolia. In more open 
spots the marsh fern (Aspidium thelypteris) is exceedingly 
abundant while the Osmundas are equally so in the tree zone. 
The lake margin is very poorly defined, the shrub zone 
being more or less predominant in different localities. The 
most typical forms near the water margin are Potentilla 
palustris, Menyanthes trifoliata, Dulichium spathaceum, 
Lysimachia thyrsiflora, Cicuta bulbifera and Scutellaria 
galericulata, while the creeping snowberry, Chiogenes 
* JOHANNSEN, Plante fysioligi. 324. 
+ WarMING, Plantesamfund. 150. 
¢ Nixison, H., Einiges uber die Biologie der schwedischen Sumpf- 
pflanzen. (Bot. Cent. 76:9). 
