EFFECT ON TRANSPIRATION. 15 



EFFECT OF SALTS WHEN PRESENT IX AMOUNTS TOO SMALL TO PRODU4 E 



BLOOM. 



Wheat (Triticum durum) was also used in the experiments to 

 <l»'t ermine the effect upon transpiration of a mixture of soluble salts, 

 chiefly sodium chlorid, when present in the soil in quantities too 

 small to produce any perceptible modification in the structure of 

 the plants. As in previous experiments the seed was germinated 

 and the seedlings were grown in the soils tested. 



All plants were grown either in paraffined wire baskets or in glass 

 jars, so that there was in no case any possibility of loss of water 

 through the bottom or sides of the vessels. Five plants were grown 

 in each vessel. Just previous to weighing, the pots were sealed over 

 by means of paraffined paper, thus reducing to a minimum the possi- 

 bility of loss of water except through the surface of the leaf. 



The water lost by transpiration was determined by weighing the 

 pots with the plants in them, the weighings being made at intervals 

 of four to eight hours during the day for a period of two or three days. 

 After the final weighing the area of the leaf surface was determined 

 by making impressions of the leaves on solio photographic paper. 

 The photographic paper was then weighed. The area of the leaf 

 surface was then cut from the photographic paper and the remaining 

 portion weighed. From the weight of the original photographic 

 paper which was found by measurement to contain a certain num- 

 ber of square centimeters and the loss of weight after cutting out 

 the impression made by the leaves, the actual area of the leaf surface 

 could readily be calculated. The amount of water lost by transpira- 

 tion could therefore be expressed in milligrams per square centimeter 

 of leaf surface per hour — the unit which will be used in the discussion 

 that follow.-. 



Two series of experiments were conducted with wheat in natural 

 soils containing, respectively, 0.09 and 0.12 per cent of total salts and 

 estimated to contain, respectively, 0.06 and 0.08 per cent of sodium 

 chlorid. These concentrations were obtained by thoroughly mixing 

 the requisite quantity of garden loam with alkali soil obtained near 

 Salt Lake City, Utah, the percentage of water-soluble salts present in 

 the soil as thus made up being determined by means of the electro- 

 lytic bridge. The controls were grown in the pure garden loam. 

 An examination of the plants grown in the alkali soils showed that 

 the bloom was very slightly developed, probably not to a sufficient 



134 



