42 Bulletin of Wisconsin Natural History Society. Vol. 1, No. 1. 
tude farther inland. Of plants occurring in Milwaukee County, 
which properly belong farther south, the button bush {Cephalan- 
thus occidcntalis) has already been mentioned (8) . Possibly the 
beech should be counted in this category. I have little doubt that 
numerous species of this kind can be found if the attention of col- 
lectors is directed to it. 
It may be worth while to state in this place the law of tem- 
perature influence on distribution of life forms as formulated by 
the Biological Survey Division (9). 
According to this formula, the northward distribution of ter- 
restrial animals and plants is governed by the sum of positive 
temperatures for the entire season of growth and reproduction ; 
the southward distribution is governed by the mean temperature 
of the six hottest weeks of the year. This accords exactly with 
the observations regarding Northern species along the lake shore ; 
for it is precisely the heat of summer which is reduced by its in- 
fluence. But it does not seem to tally so well with the occurrence 
of Southern forms, for the sum of temperatures during the grow- 
ing period is certainly not increased by the lake influence. Per- 
liaps rnodifications of the moisture relations have something to do 
with this. At any rate, a wide field for interesting and profitable 
study is here opened. 
8. This occurs, however, several miles away from the Lake shore. 
9. National Geographic Magazine, Vol. VI.. page 229. Merriam, Life Zones 
and Crop Zones, Bulletin 10, Div. Biol. Surs-ey. 
