24 BULLETIN 211, U. S. DEPARTMENT OF AGRICULTURE. 



Of more importance is a group of introduced weeds, about the 

 probable effects of which we know less and whose spread within 

 recent years has been rather ominous. These are mostly tumble- 

 weeds, of which the Russian thistle (Salsola pestifer) is far and away 

 the worst. (PI. VII, fig. 1.) Their seed-distribution habits are 

 admirably adapted to an open country with strong winds, and they 

 scatter their abundant crops of seed over wide areas. Most of the 

 species are able to endure extreme drought and great heat; their 

 seeds germinate readily and the seedlings endure very unfavorable 

 conditions and grow into plants that mature seed whether they be 

 but a few inches high or reach maximum size. They practically all 

 belong in the goosefoot or amaranth families and have to their credit 

 the fact that they are all to some extent valuable as forage when 

 young, and they are eaten when nothing better is available. 



In regions having a rainfall of over 15 inches the Russian thistle 

 is very much at home, and wherever the native grasses have been 

 killed out either by stock or by the plow it is a pestiferous weed. 

 For a shor£ time, while it is young and tender, it is a fairly good 

 feed, and it has been used as hay and silage when other crops have 

 failed in the dry-farming regions; but these uses are always make- 

 shift attempts to utilize a product that is not desired. Ordinarily, 

 it does not seem to be able to crowd out the native grasses, but in 

 the dry-farming areas, where the sod has been broken and the land 

 deserted for any reason, it usually takes the ground completely. It 

 also takes badly overstocked places on the ranges, especially where 

 sheep have been held too long. Whether the native grasses will be 

 able to crowd their way back into such areas or not still remains to 

 be seen. If they are not, then the importance of this pest is in- 

 creased many times. 



Certain poisonous plants are also of some considerable menace to 

 the ranges, especially where any overstocking is going on. Speaking 

 very generally, these plants form a very small and numerically unim- 

 portant part of the natural flora until the factor of overstocking 

 enters. Of course, the different species differ in importance merely 

 on the basis of the readiness with which they reproduce themselves 

 and their ability to compete with their plant associates. Under 

 normal conditions, unless pressed by hunger, grazing animals of all 

 kinds let them alone and hence do not in any way interfere with 

 their natural rate of reproduction and spread. Like other weeds 

 that are not eaten, they thus tend to spread much more rapidly 

 when relieved of their plant competitors by the animals. In fact, 

 under these circumstances there is nothing left but their animal and 

 plant parasites to hold them in check, unless man should interfere. 1 



1 A few species of loco weed have become so abundant on some of the sheep ranges of California that it 

 is now the custom in certain localities for the herder to carry a spud or a spade, dig these plants up, collect 

 them, and burn them. The practice evidently pays or it would not be followed. 



