16 



BOTANY OF L,A SAL,LE COUNTY. 



then very little until October or November. Besides 

 the rains thunder showersof the spring- and summer 

 are generally local, being 1 often confined to narrow 

 strips of country, so that the moisture is very unevenly 

 distributed. We have records of rainfall for Ottawa 



only. 



Rainfall for each month of the year given from ob- 

 servations of Dr. J. O. Harris, Ottawa, 111: 



The country six to eight miles north of Ottawa fre- 

 quently has heavy showers in the summer when no rain 

 falls at Ottawa. At times showers seem to follow 

 the Illinois valley, and often one seems to divide west 

 of the Big Vermilion and one part of it to go along the 

 Illinois, the other to keep south of the ridge east of 

 the Big Vermillion. 



The country south of the Illinois river and for 3 or 

 4 miles north of it seems to receive less rain and to 

 suffer more from drought than that farther north and 

 cyclones have visited no parts of the county except 

 the extreme northern in Meriden and ICarl townships. 

 Hailstorms are not common. On one occasion much 

 harm was done vegetation to the west of the Big Ver- 

 million and twice we have seen the tracks of destruc- 

 tive hail storms in Northville township. 



The rainfall during thunder storms is sometimes ex- 

 cessive and causes tremendous floods in the small 

 streams, which are sometimes swollen to 10,000 times 



