PLANT GROWTH IN DRY AREAS 117 



plane over .which those that come later roll, and speed on 

 their way to farther distribution. Fortunately nearly 

 all this class of weeds is short lived or at least compara- 

 tively so, and they are more easily destroyed than some 

 other forms of weed life. Wild oats. and mustard and 

 other seeds are frequently carried by the winds from one 

 farm to another that happens to lie adjacent to it on 

 the leeward side. Fortunately water is not an important 

 agent in carrying weed seeds in dry areas as it frequently 

 is in humid areas and also wherever irrigation is prac- 

 tised. 



Certain forms of weed life are more difficult of eradi- 

 cation in dry than in humid areas. This is especially true 

 of weeds the seeds of. which have much oil, as for in- 

 stance wild mustard and penny cress. The small amount 

 of moisture relatively that is in the soil tends to 

 prolong vitality in the seeds. Because of this, weeds will 

 grow after longer periods of burial- in such soils than if 

 buried in soils more humid. Of course as long as seeds 

 retain vitality they remain ready to grow when subjected 

 to favorable conditions for growth. 



It shoulder be easier nevertheless to maintain clean- 

 liness in farms in dry than in humid areas, owing to the 

 character of the rotation. The farmer in dry areas is 

 compelled to give much attention to summer-fallowing 

 the land, or to growing cultivated crops, or to both, in or- 

 der to secure the requisite amount of moisture. If this 

 work is faithfully and intelligently performed, and 

 proper attention is given to the cleaning of the seed 

 used, it should be quite practicable to keep farms prac- 

 tically free from noxious weeds. Nowhere else where 

 farming is conducted, should the farms be so free from 

 weeds as in dry areas. 



Grain plants volunteering. The tendency in cereals 

 to volunteer is ever present in dry areas. Volunteer 

 grain means grain that grows from seed that has shat- 



