PAPERS OX BIOLOGY AND AGRICULTURE 169 



The upper flood plain is found in a narrow band on 

 the east and north banks and at the west end. This area 

 is rather wider than would be expected because when the 

 pond was lowered, this society advanced and the outer 

 boundary, owing to the adaptability of the species, re- 

 mained the same. The species that characterize this 

 society are, Ambrosa trifida (great ragweed), Arctium 

 minus (burdock), Ulnus americans (elm), Salix longifolia 

 (sand bar willow), Populus deltoides (cottonwood), 

 Arena sativa (oat), Taraxacum officinale (dandelion), 

 Trifolium repans (white clover), Xepta cartaria (cat- 

 nip), Lepidium capsella, Lactuca integrate (wild lettuce), 

 Trifolium pratense (red clover), Plantago rugelii (plan- 

 tin), Salix alba (white willow), Asclepias syriaca (milk- 

 weed), Tradescantia virginiana (spiderwort), Postinaca 

 sativa (wild parsnip), Cercium lanceolatum (common 

 thistle), Poa pratensis (Kentucky blue grass), and Hore- 

 doum jaubatum (wild barley). The willows and elm trees 

 at the west end are scrubs, but around the steeper banks 

 on the east and north sides we find seedling cottonwoods 

 and willows about three to five years old. 



Lake Knox is an artificial pond. The banks on three 

 sides are composed of rubbish and ashes dumped there 

 when it was formed. On the south embankment, the rail- 

 road company periodically dumps ashes and cinders on 

 the lake side. These layers have a very disastrous effect 

 upon the vegetation on the bank and in the water. These 

 cinder patches on the bottom of the pond give no foot- 

 hold for the emergent aquatics. The few more hardy 

 terrestrial types that are able to exist under these con- 

 ditions are sand bur, smartweed, burdock, and if the bank 

 is not disturbed in the spring, the great ragweed. Six 

 sand bar willows and an elm have been struggling for 

 several years to keep above the cinders. Only last month, 

 the Street Railway Company dumped two or three car 

 loads of brick and sand on the bank and into the pond at 

 the north east corner. A scrub willow growing there is 

 surrounded completely by about 12 inches of this materi- 

 al and the small willows near by have been obliterated. 



