FLOWEEIXG PLANTS AND FERNS OF INDIANA. 589 



Russian thistle were taken from the field. The farmer should be con- 

 stantly upon the alert for the first appearance of these strange plants 

 and should promptly destroy any suspicious form. It is at the time of 

 the first appearance of a weed that the work of control should begin. 



A weed, also, if it rises to the rank of a "bad weed," must be able to 

 maintain itself against enemies in the form of browsing animals. This 

 defense may be secured in manifold ways. It may be through defen- 

 sive armor, as in the thistle, through a thick covering of hairs, as in 

 the mullein, through a toughness of fiber, as in most composites, 

 through an acrid juice, as in the smartweeds and spurges, or through 

 irritating mineral crystals, as in the Indian turnip. If, in addition 

 to the power of adaptation mentioned above, the plant by any means is 

 able to repel browsing animals, it has gained an immense advantage 

 in the struggle for existence, and is on the high road to weed eminence. 



Plants, also, have other means of propagation than that furnished 

 by seeds. Many of our worst weeds are such because they multiply 

 not merely by means of seed, but also by means of root stocks or run- 

 ners. In cases of this kind, mere destruction of the seed will not serve 

 to exterminate or even limit appreciably the spread of the pest. Be- 

 fore any rational method of extermination can be employed, it is 

 evidently necessary to understand the means by which the particular 

 species is propagated. 



In many weeds, the annoying abundance is due to the means of dis- 

 tribution of the seed and fruit. Beggarlice, burdock, Spanish needles 

 and sticktights cling to the coats of stock and are thus distributed; 

 the milkweed, the thistle and a host of other composites are distributed 

 by the wind, while other forms are distributed by birds and grain- 

 eating animals. 



A weed is a weed, therefore, because it has a wide range of adapta- 

 tion in respect to physical factors, possesses efficient defensive devices, 

 propagates readily, often by several methods, and has, as a rule, espe- 

 cially effective means of seed dispersion. Any plant possessing these 

 properties is liable to become troublesome. 



In a general way it may be said that the chief characteristic of weeds 

 is a rapid and vigorous stem growth. In case the stems are erect this 

 rapid growth brings the plant into the proper light relation and serves 

 at the same time to shade other plants and retard their growth. Where 

 the stems are not strong enough to maintain themselves in an erect 

 position, they may form a mat or carpet over the ground, thus smoth- 

 ering plants of a slower and less vigorous stem growth. 



As the proper time to combat a weed is upon its first appearance, 

 the landowner should know the plants of his farm well enough to rec- 



