172 BOTANICAL GAZETTE [mance 
adequate to account for the great differences, and it may be that 
climatic or other less apparent factors may have to be called 
upon. The luxuriance of the northern forests as compared with 
those about Chicago may need in part a similar explanation. 
Interesting beach conditions are to be found on some smal’ 
islands that have recently formed on reefs in the vicinityol 
Beaver island. During the winter and spring blocks of ice laden 
with stones are stranded on these reefs ; thus they are gradually 
built up to the lake level. Wave action comminutes the reef 
materials forming a soil suitable for plant life; the waves and 
winds also constantly add to the area of the islands. One such 
island is about 200 meters in length, five or ten meters in width, 
and scarcely thirty centimeters high. The flora of this ump 
tected island is a swamp flora, 7. ¢., the island is in its entirety 
hydrophytic beach. Another island, somewhat larger and Col 
siderably older, has an altitude of one or two meters at its high 
est point. The beach toward the southeast, east, and northeast 
is hy drophytic, while that toward the northwest, west, and south 
west is xerophytic. Undoubtedly the degree of exposure to the 
wind is the chief cause which determines the nature of the flora 
on this island. Not only is the wind more severe on the wes 
beach, but the waves pile up more sand on that side of the island 
and hence produce a drier soil. The flora on this xerophyt 
upper beach is remarkably complete and diversified, showing 
distinct zonal distribution. Above the middle beach there oe 
zone characterized by the dominance of Elymus Canadensis, thes 
a zone of Geranium Robertianum, then a zone of Artemisia ee 
densis, and finally a zone in which Cornus stolonifera (or C. ee 
into which it grades) is the chief character plant. Seatté 
more or less with these are Prunus pumila, Enothera bienmis, p 
rus Maritimus, Cnicus Pitcheri, Agropyrum dasystachyum, and a 
lus balsamifera, Pastinaca sativa and Geranium Roberta 2 ic 
common here, and are remarkable inhabitants of @ err 
beach, since both are usually inland mesophytes. Two oa 
plants occur on this beach that are south of their chief range 
Tare in the Lake Michigan region, Tanacetum Huronenst 
