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above in search of moisture ; but when we remember that this 

 small pipe, four inches in diameter, drains two chemical labor- 

 atories running at their full capacity during the entire school 

 year, a different aspect is placed on the phenomenon. No less 

 than 150 pounds of sulphuric acid alone pass through the pipe 

 during the year. Of course there are solutions of other acids 

 and salts in corresponding quantities. At certain times in the 

 year and indeed at different hours of the day, solutions of 

 poisonous chemicals of considerable density must pass down 

 this pipe and bathe the roots which project into it. 



There are probably two reasons why the large root of the 

 Virginia creeper should follow the pipe. It found along this 

 path considerable moisture and but slight resistance compared 

 with the hard undisturbed caliche on the outside of the trench. 

 But since we are naturally led to suppose that its main object 

 was a search for water, we may inquire why it did not follow the 

 pipe closely instead of remaining at a distance of one to two 

 inches. The probable explanation for this is that it kept a safe 

 distance from the poisonous chemicals which flow down the pipe 

 and that the small quantities which ooze through the loose joints 

 are reacted upon to some extent by the soil which renders them 

 less harmful. Possibly the laterals which entered the pipe did 

 so at a time when the quantity of chemicals in solution was at 

 a minimum, as is the case during the summer months. One of 

 the rootlets which entered the pipe a distance of half an inch was 

 in apparently a perfectly healthy condition but the other which 

 entered a distance of fully an inch had its end blackened and 

 dead. 



The roots which formed a mat around the joints and were the 

 chief agents in clogging the pipe proved to be those of Bermuda 

 grass (Capriola Dactyloii) a plant which does not appear at all 

 choice with reference to what it drinks, for it is known to thrive 

 in the Southwest in localities where alkali is very abundant. 

 Among other plants growing in the vicinity and which doubtless 

 contributed to some extent to the clogging may be mentioned 

 burr clover, alfalfa and rescue grass. 



University of Arizona, February, 1901. 



