46 
IOWA ACADEMY OF SCIENCE 
There are few weeds of the Rose Family. The Silver Weed {Poten- 
tilla anserina) is common in IManitoba and provinces westward, especi- 
ally in alkali impregnated soils. The Common Fivefinger (P. mons- 
peliensis)^ is not common in the northwest provinces bnt common in the 
northern and eastern states. The Western Fivefinger (P. (Mssecta) is 
also common in the northwest especially westward. 
Of the Y ertenaceae there are no common weeds in iManitoba to the 
Pacific coast. Three species are troublesome in Iowa and Minnesota, 
the Verbena strict a, Y. hast at and Y. nrticaefolia, and the Y. hracteosa 
is a common roadside weed in the Mississippi Valley and eastward. 
Weed migration is an interesting problem and the northwest is of 
partcnlar interest because a virgin soil is being turned under to pro- 
duce agricultural crops. What weeds will succeed best in a country with 
the climate and rainfall of Canada should be f ollow^ed up by the Canadian 
botanists. 
Dr. C. H. Shaw^ in an interesting communication on ‘‘The Causes 
of Timber-line on Mountains,” shows how through human agencies in 
the Alps of Switzerland, the vegetation has become changed in a very 
marked degree. The whole aspect of our prairie flora in Iowa is chang- 
ing and before many years that of the northwest will be very different 
from its character today. 
^Plant World 12: Aug. 1909. 
