IOWA ACADEMY OF SCIENCE 
35 
nadian Thistle are more common. Different crops and different regions 
produce weeds which may become locally prominent. In southern Iowa 
the Horse Nettle and Cocklebur ‘are more abundant than in Northern 
Iowa. In Avestern loAva the Marsh Elder {Iva xanthiifolia) is an immi- 
grant from the AA^est, and it has extended northAvard into Canada. In 
the Red River Valley of the North, the Iva xanthiifolia known locally 
as the half-breed AA^eed is abundant. One sees, hoAvever, little of such 
common loAA^a AA^eeds as the MayAA^eed (Anthemis Cotula) and Butter- 
print or Indian klallow {Ahutilon Theophrasti) . Nor is the large Rag- 
Aveed (Ambrosia trifida) as common as in loAAm. The AAMolly Thistle 
(Cirsium canescens) is abundant. 
As Ave cross the boundary line or approach it, Ave see that one of the 
native shrubs of that country (Eleagnus argentea) spreads rapidly AAdiere 
the surface of the soil has been removed, very much as the cottomvood 
does in loAva or in other parts of northern United States. 
In the country from 'Winnipeg to Vancouver and the Rocky Mountain 
states, the common Scpiirreltail Grass (Hordeum jiibatum) is one of the 
most striking Aveeds in fields and Avaste places. At is, of course, a strik- 
ing, Aveed also in Iowa, but it Avas rare here prior to 1876. Cultivation 
and neglect of tillage has caused these Aveeds to become extensively 
scattered. AA^eeds adapt themseUes to conditions most suited for their 
eiiAuronment and it strikes one as peculiar that the most common ruderale 
plants of loAva, like the Green Foxtail and Pigeon Grass, as Avell as the 
Crab Grasses are as yet of little importance in the Canadian NorthAvest 
although troublesome in the Alississippi valley. They occur across the 
continent and on the Pacific coast but do not coA^er the ground as they 
do here. To the south in Montana, Idaho, and especially Colorado and 
Utah, they have become common. The AVild Oats (Avena fatua) is 
common in the northAvest as it is in parts of Alinnesota and the irrigated 
districts of the Rocky Alountains, largely because the Aveed is spread Avitli 
the culture of oats. The Holy Grass (Hierochloe borealis) a Avell knoAAui 
native grass of the north is comparatively rare in Iowa, except north- 
Avard and it is not knoAvn to be Aveedy in that section of the state. Hoav- 
ever, in the Canadian nortliAvest it is a persistent and troublesome 
perennial Aveed. Other someAvhat Aveedy grasses are AAAmless Brome 
Grass (Bromus inermis) , Commmon Cheat (Bromus secalinus) and the 
Darnel (Lolium temidentum) . Today it is difficult to find common 
Cheat in many parts of loAA^a largely because Ave no longer groAV AApeat 
but the Soft Chess (Bronins mollis) is coming in rapidly. In Utah the 
Bromus tectorum and Hordeum murinum have become most troublesome 
