24 BOTANICAL GAZETTE [yuLy 
THE BORDER ZONE 
The outermost growth which immediately borders the open 
water and forms a more or less broken fringe around the island is 
for the most part hydrophytic. Along the southern shore it is 
dominated by the swamp loosestrife (Decodon verticillatus) and in 
places by cat-tails (Typha latifolia and T. angustifolia). This 
facies has for its principal and secondary species Hibiscus Mos- 
cheutos, Sagittaria latifolia, Polygonum hydropiperoides, Ranun- 
culus pennsylvanicus, Scutellaria galericulata, Lathyrus myrtifolius, 
Bidens cernua, Potentilla palustris, Campanula aparinoides, Galium 
triflorum, Cicuta bulbifera, Peltandra virginica, and others. They 
are generally abundant, with Decodon and Typha forming a dense 
growth, which attains a height of 2-6 feet (0.6 to 1.8 m.) above the 
substratum. The vertical zonation is that of the differences in 
habit of growth of the individual species. The members differ 
widely from one another both in external features and in their 
demands upon the environment. In these regards the vegetative 
shoots adapt themselves little to the prevailing exposed conditions. 
Growing upon a peat substratum whose depth and physical char- 
acteristics are in every way like that of the other plant zones to be 
described below, the xerophytic type and quality are least marked 
in this vegetation. The well decomposed peat soil of the border 
zone permits here a luxuriant growth. The plants are able to 
secure all of their raw food materials from the water and air, and 
build their own substratum. The high water capacity of peat, 
the absence of a mineral soil, the smaller percentage of oxygen 
in the water, and the incoherency of the substratum afiord no 
precarious conditions for growth. Here the toxicity of the sub- 
stratum and the consequent physiological aridity are least marked. 
It is evident that dilution and the capacity of absorption of 
soluble salts by the humus soil along ue margin (8, p. 403; 9) 
corrects any harmful effect. 
The Decodon-Typha association has a transition appearance, 
for a considerable admixture of plants such as Rosa carolina, 
Cephalanthus occidentalis, Cornus canadensis, C. paniculata, C. 
stolonifera, Salix discolor, S. nigra, S. pedicellaris, Alnus incana(?), 
A. rugosa, Ilex verticillata, Prunus melanocarpa, Rhus Vernix, 
