62 \ VTIVE VEGETATION AS AN INDICATOR 



passed when only a few scattered or stunted plants are 

 found. Generally when such scattered alkali-indicating 

 individuals are found the soil contains some alkali, but the 

 quantity is not clearly indicated. It is only when the 

 plants produce a vigorous growth and occupy the land to 

 the exclusion of non-resistant if not all other species of 

 plants - that they may be taken to indicate the kind and 

 quantity of alkali characteristic of their species. 



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. | 







Fig. 9. Alkali Land which is Indicated by the Growth 



of Shadscale. 



It should be kept in mind also that under certain condi- 

 tions alkali-indicating plants may grow well where alkali 

 may not be present in quantities injurious to general 

 crops and that non-resistant plants may be growing well 

 on land so strongly impregnated with alkali that farming 

 would be practically impossible without reclamation. 

 Such conditions as a shallow hardpan, a dry sandy layer 

 of soil, or other conditions which cause the plants to suffer 

 for w r ant of water, as they do when in the presence of ex- 

 cessive quantities of alkali, may allow the presence of the 

 alkali-resistant plants in abundance to the exclusion of 



