70 Plant Tissue Culture 



dem. The best procedure appears to be to start 

 with ''tap water" from a spring or well (city 

 water frequently contains chlorine which may 

 pass over in the still and reappear in the product 

 unless the condenser is properly vented). This 

 should be treated with a softener and filter to re- 

 move the greater amount of dissolved salts, oil 

 from pumps, particulate matter, and other prod- 

 ucts which might interfere with the efficiency of 

 the first distillation. It should then be distilled 

 with an ordinary well-vented still and should 

 finally be passed into a second still, re-distilled, 

 and the final product collected in Pyrex contain- 

 ers. A block tin still of the "Precision" type, if 

 properly handled, is quite satisfactory for the 

 final distillation for all ordinary purposes. A 

 Pyrex still can also be used. Distillation in 

 quartz, silica, silver, or other special types of 

 stills will seldom be necessary. Special precau- 

 tions to insure removal of traces of particular ele- 

 ments may have to be taken in special cases — thus, 

 Pyrex can, of course, not be used for storage of 

 water to be used in any critical experiments on 

 the behavior of tissues towards boron, rubber 

 tubing or stoppers should not be used in experi- 

 ments with zinc or sulfur, and so on (Anion, 1938, 

 133; Arnon and Stout, 1939, 134, 135; Stout and 

 Arnon, 1939, 140; Hoagland and Arnon, 1941, 



