40 WHEAT EESISTANCE TO TOXIC SALTS. 



This is probal)ly an error so far as young seedlings are concerned. 

 The seed contains everything necessary for the early grovrth of 

 the plant, and the absence of all minerals or other nutrient com- 

 pounds in the surrounding solution should produce no bad effect 

 during the earliest stages of growth. Those who claim that dis- 

 tilled water is injurious will probably find, upon closer observa- 

 tion, that it is some injurious substance in the water which is really 

 toxic to the roots. In the case of many plants one of the most toxic 

 substances known is copper, and it is more than likely that it is 

 present in much of the water which experimenters have found to be 

 injurious. Coupin states that one part of copper to 700,000,000 of 

 -water is sufficient to retard the root growth of wheat seedlings. A 

 mere trace of copper is sufficient to retard growth in many cases. 



As a result of an analysis made in the Bureau of Chemistr}^ of the 

 Department of Agriculture of the distilled water used in these 

 experiments, it Avas found to contain a considerable quantity of zinc, 

 but no trace of copper. The harmful effect probably should be 

 attril)uted to zinc alone. The water used in these experiments was 

 distilled but once, and was collected in a porcelain tub as a receiver. 



It was thought while the work with wdieat seedlings was in prog- 

 ress that copper or zinc might be the cause of the injurious effects, 

 but the writer used the water from the same still for all experiments 

 with Lupinus albus, and no toxic effect of the distilled water was 

 noticeable. Control checks with lupines were carried in both dis- 

 tilled and hydrant Avater, and no difference was found in the rate of 

 growth. It was this observation which at the outset of the work with 

 wheat gave the writer confidence in the quality of the distilled Avater. 

 This is apparently another indication that different species of plants 

 vary greatly in their ability to resist the influence of toxic salts. 

 Wheats are apparently much more sensitive than lupines to pure 

 solutions of zinc salts, although nuich less sensitive to pure solutions 

 of sodium and magnesium salts. 



At first thought one would conclude that since the distilled Avater 

 used contained harmful substances the experiments aboA'e described 

 are practically Avithout A'alue; but such is not the case, as aaIII be 

 seen before this discussion is completed. In order to compare closely 

 the Avater used during most of the experiments Avith absolutely pure 

 water, some exi^eriments Avere made. To secure absolute purity in 

 the water a ncAv still was made of the best nonsoluble glassware, hav- 

 ing no metal in any of its parts. The same AA'ater that had been 

 previously used Avas redistilled for the purpose. The Avheat seedlings 

 AA'ere treated in CA'ery AAay as before. A control Avas also carried in 

 Potomac Eiver Avater for comparison, and each lot of seed was taken 

 up each day and the elongation of the roots measured and recorded 

 for four consecutiA'e daA^s. In the tAvice-distilled Avatcr they grew 



