83 



disappeared, and 6 ha\'o ininiigraUd in three years. These are 

 Arenaria serpyllifolia, Dactylis glomerata, Phleum pratense, 

 Lepidium virginicum, Rumex acetoseUa, and Trifolium repens. 

 Arenaria is the only one of these which does not occur elsewhere 

 in the immediate vicinity. 



In the small dooryard of an abandoned Indian hut, where 15 

 species occurred in 1914, the number has been reduced to 9. 

 No new species has been added, while Achillea millefolium, 

 Chenopodium album, Dianthus harhatus, Lepidium virginicum, 

 Rumex acetoseUa and Trifolium pratense have disappeared. 



On the grounds of the biological station 21 species were re- 

 ported in 1914, while only 13 occurred in 1917. This involves 

 no new additions, but the loss of eight species: Avena saliva, 

 Brassica arvensis, Polygonum Convolvulus, Secale cereale, Setaria 

 viridis, Silene noctiflora, Trifolium pratense, and Verhascum 

 Thapsus. 



The greatest change in the flora was observed in an isolated 

 clearing in a cedar swamp, occupied by an old man throughout 

 the year, and by one family during the summer months only. 

 Nine of the 24 species listed there in 1914 have disappeared, 

 while 17 spec'es have immigrated. In 1914, 5 of the species 

 were not known elsewhere in the uncultivated region ; these have 

 all disappeared. Of the new immigrants, Melilotus alba, Poly- 

 gonum pennsylvanicum, and Satiireja acinos are not now reported 

 from any other stations within the area. 



All of these several stations show as before the close dependence 

 of introduced species on human activities. They also indicate a 

 considerable fluctuation in the flora from year to year, involving 

 the loss of some and the addition of other species. In general, 

 the additions are greater than the losses, showing the cumulative 

 effect of intercourse with the villages and agricultural districts 

 on both sides. 



A number of causes might be mentioned as possibly contrib- 

 uting to the loss of species, such as hoeing, mowing, or grazing 

 at critical periods in the development of the plants, unfavorable 

 climate, or competition with other species. Continuous obser- 

 vation throughout the season would be necessary to verify any 



