WEEDS OF MONTANA. 13 



The following, supposed to be natives of tropical America, 

 are now common over much of the Eastern United States, and, 

 with many of the weeds of the plains, are probably our inheri- 

 tance from the prehistoric American civilizations. 



Amaranthus chlorostachys, Willd. Erigeron Canadensis, L. 



A. retroflexus, L. Solanum rostratum, Dunal. 



Ambrosia artemisiaefolia, L. Xanthium Canadcnse, Mill. 

 A. trifida. L. 



All the other species enumerated in this paper, with two or 

 three doubtful exceptions, are from the Old World and have 

 reached us mainly from the Eastern States. 



THE ROOT SYSTEH. 



The root system is of great importance as indicative of the 

 life duration of a species and hence must be taken into account in 

 fixing upon methods for weed extermination. 



An annual plant germinates, bears fruit and perishes in a 

 single season, while a biennial bears only a tuft of leaves the first 

 year and fruits and dies the second. A perennial species lives and 

 bears fruit for many years in succession. The roots of annuals are 

 tender and of about the same size as the stem; biennials are 

 usually tender and often thickened and fleshy, but are sometimes 

 difficult to distinguish from annuals, otherwise than by observa- 

 tion, while a number of weeds appear to be either, as emergency 

 requires. Perennials usually have thick, woody, deeply penetrat- 

 ing roots, or long underground stems, or tubers, which enable 

 them to endure indefinitely. The weeds in cultivated ground are 

 mostly rapid-growing annuals, or perennials with fleshy or tuber- 

 ous roots or rootstocks; those of pastures and meadows are 

 perennials almost exclusively and cannot withstand cultivation- 



CLASSIFICATION BY SITUATION. 



Weeds may be grouped roughly by means of the localities they 

 affect and the causes that make them objectionable. 



I. Weeds of Yards, Waysides, and Waste Places.— These 

 are often tall and unsightly or tend to spread to adjacent fields 

 and gardens. They replace the native plants exterminated by the 

 feet of man and the domestic animals and the wheels of vehicles. 



