Nov., 1910.] A Floristic Survey of Orchard Island. 201 



There is a sparse growth of shrubs, Rubus nigrobaccus, Rhus 

 glabra, R. toxicodendron, Vitis vulpina, etc. The herbage is 

 also poorly developed, it consists of a thin growth of grass and 

 common weeds which have been frequently mowed and in some 

 places burned. A narrow border of larger trees, remnants of the 

 original forest, surrounds this central area. On the south and 

 west this forest border is twenty to thirty feet wide; but to the 

 north and east there is sometimes but a single tree, the lawns 

 extending to the water's edge. 



An interrupted zonation of swamp plants occupies the shallow 

 water and the now exposed mud plain surrounding the island. 

 The swamp is well developed on the west, south and southeast, 

 but has been more or less completely cleared away in the vicinity 

 of the docks on the north, northeast and east sides. 



This island exhibits a striking example of the invasion of plants 

 into new areas, successful ecesis, the resultant succession, the con- 

 seciucnt filling of the lake and the upbuilding of new land areas 

 along the margin; and in the center a secondary succession in a 

 partially denuded area. A detailed floristic study was made of a 

 belt sixt}' feet broad and extending directly across the island from 

 the southeast to the northwest, from a-a' to b-b' on the map. 

 This belt covers a representative area of the island, including a 

 section of the well developed marsh on the southeast, and on the 

 northwest the marsh disturbed and reforming; a section of the 

 older forest zone and of the rejuvenated central area. 



There are three distinct formations based on habitat and 

 growth fonns: 



I. The marsh-herb formation. 

 II. The swamp-shrub formation. 



III. The mesophytic-forest formation. 



The first and third formations are well developed, the first 

 exhibits a striking lateral and vertical zonation, the second is so 

 fragmentary that it can scarcely be dignified by the name of 

 formation; but it is of interest as an illustration of the intrusion 

 and development of a zone between two previously existing ones. 

 I. The marsh-herb formation on the southeast: 



1. Nelumbolutea Society. 

 Fades. 



Nelumbo lutea. 



Secondary species. 



Potamogeton pectinatus. Potamogeton natans. 



Potamogeton var. Cladophora sp. 



Ceratophyllum demersum. Spirogyra sp. 



The society forms a zone 20-40 feet broad. At the outer 

 margin the water is 4-4.5 feet deep at the inner about 8 inches. 



