36 
IOWA ACADEMY OP SCIENCE 
weeds and rapidly spreading to Colorado. With ns the H. pusilkmi is 
making its way northward into Central Iowa. 
The next great family of interest is the Composite Family ; the plants 
are plastic and aggressive, the old world species more so than those of 
the new world. In Iowa most of our composite weeds are from the old 
Avorld hut in the Canadian Northwest and in the West there are many 
indigenous native species. The Gum-wood, {Grinclelia squarrosa) al- 
though I have known it for some years in Central Iowa, is not spread- 
ing. This weed is common from Winnipeg westward through the Rocky 
iMountains south to Minnesota and Western Iowa. However, it is not 
persistent in cultivated fields. The most aggressive of the native weeds 
is iMarsh Elder, {Iva xanthiifolia) though extending eastward to the 
Mississippi River it is not- important in the Eastern states, it partially 
takes the place of the Large Ragweed in the Missouri Valley, the Red 
River of the North and in Manitoba. This weed illustrates how a plant 
common in the alluvial fiood plains soon adapts itself to cultivated 
areas. The older settlers of Manitoba always found it near buildings 
occupied by half-breeds^ but presumably also by other untidy farmers, 
and hence have given it the name of ^Gialf-breed weed.” 
The Yarrow, an indigenous plant, is abundant throughout the region 
from Winnipeg to Seattle, although rarely troublesome in fields. The 
Greater Ragweed, {Ambrosia trifida) one of the most conspicuous weeds 
in the Northern Mississippi Valley, is fairly common in the southern 
part of Manitoba to Winnipeg, St. Vincent, Minnesota, and Pembina, 
North Dakota. Outside of the Province of Manitoba it is a rare weed. 
The Ilog-weed or Bitter- weed {A. art emmac folia) is still rarer, but 
the perennial A. psilostachya is not infrequent in Minnesota and in 
gravelly knolls of Iowa, and is a fairly common native plant on the 
plains about AA'innipeg, westward it is not common, though common in 
the United States east of the Rockies. The common IMayweed {Antli- 
emis Cotula) and Burdock (Arctium major) of Iowa, AABsconsin and 
Minnesota, are comparatively rare in the Northwest territory but 
more frequent on the west slope of the Rockies in British Columbia, 
AA'ashington, Oregon and Utah. This is particularly true of the Bur- 
dock. The indigenous biennial Wormwood (Artemisia biennis) is quite 
as common in Manitoba as in Minnesota, while the European AVorm- 
wood (Artemisia vulgaris) is a common plant along roadsides in Mani- 
toba. The European Mugwort, (Senecio vulgaris) seldom seen in the 
Northern Mississippi Valley states, is common in places in Manitoba, 
on the Pacific Coast, Vancouver Island and Seattle in Washington. In 
the recent edition of Gray’s Manual Robinson and Fernald note that 
