1905] BROWN—THE PLANT SOCIETIES AT YPSILANTI 281 
upon another that there have been produced areas of turf which 
otherwise would have been very limited or wholly absent. Along 
the brink of the cemetery bluff a line of tension is easily traced. It is 
not sharp like the swamp lines; but, like the usual upland type, 
there is an area over which the societies blend. Poa compressa, 
Andropogon scoparius, A. jurcatus, and Stipa spartea crowd their way 
for a distance of one to six feet into the turf of Poa pratensis and 
Trijolium repens, where they fade out altogether. 
It is plain that animal life has played an important if not a chief 
part in the dispersal of seeds in the valley. Squirrels and like animals 
were formerly more common than now, but birds are yet numerous; 
the blue-jays,3 cat bird,t and crow blackbird’ alone feed upon a 
variety of fruits that includes more than one-half of the woody 
species at the bayou, exclusive of the large trees. 
Besides these, there are the red-winged blackbird, vireo, oriole, 
woodpeckers, song sparrows, cowbirds, and robins, which are com- 
mon all along the stream and are known to devour fruits. This 
has resulted in scattering the seeds of a number of shrubs, vines, and 
small trees in the open places of the forest. At the bayou there are 
sixty-one species of this kind, 82 per cent. of which have adaptations 
for seed dispersal by animals; 72 per cent. have the brightly colored 
fruits eaten by birds, of these 22 are red, 10 black, 7 blue, and 5 white. 
It is possible that this may indicate something with regard to the 
relative attractiveness of the several colors. 
Over two-thirds of the species with colored fruits occur in the 
bluff societies, and are most numerous with the juniper, sumac, and 
8 oak. This fact is not so easily explained by any habit of the 
as it is by the character of the woods. ‘The same relations 
“ppear to hold true of corresponding societies away from streams, 
én * Beat, F. E, L., The blue-jay and its food. Yearbook, U.S. Dept. Agric. 1896: 
Se a S. D., Birds of a Maryland farm. Bull. 17, U. S. Dept. Agric. Div. 
- Survey, p. 104. 
s 
Us ase & : . L., Food of the bobolink, blackbirds, and grackles. Bull. 13, 
* Dept. Agric., Div. Biol. S 
urvey, p. 64. ; 
Nees The crow blackbirds and their food. Yearbook, U.S. Dept. Agric. 1894: 
