1917] Ayres: Nutrient Solution on Plants Grown in Sand Cultures 345 



The physical effects of sand as a medium for plant growth have 

 been shown recently in a striking manner by McCall,^^ who added 

 to sand the solutions whicli Shive^" used as water cultures, with 

 the result tliat much larger quantities of the nutrient salts were 

 required than when the same species of plant was grown in water 

 culture. The sand-culture method was selected for the present 

 work with the above evidence in mind, and also because the 

 growing period of the tobacco plant is long and this method 

 precluded the tedious changing of solutions necessary when the 

 water-culture method was used. 



Experimental Material 



The plant which was used in the present series of investiga- 

 tions was a tobacco of hybrid origin derived from a cross between 

 NicoUana sylvestris (U. C. B. G. 69/09) and Nicotiana tabacuni 

 var. macropJiylla (U. C. B. G. 22/07) and known in the Uni- 

 versity of California Botanical Garden as U. C. B. G. H38.^" 

 The plants to be used were raised from seed and were transferred 

 as seedlings to the sand from the flats in which they were grown 

 after carefully washing the roots free from adhering soil par- 

 ticles. In picking out seedlings from the flats care was taken to 

 choose from the large number of plants available only those 

 which were most nearly uniform with reference to size and 

 general appearance. The plants were kept during the experiment 

 in a well-ventilated greenhouse. 



The sand used was a light-colored beach sand which on 

 analysis by means of the acid-digestion method of Hilgard showed 

 the following composition : 



The water-holding capacity was 22 per cent when saturated. 

 The sand was prepared for the experiment by washing in a 

 heavy stream of tap water which was allowed to percolate through 



1'^ Unpublished work. 



18 Loe. eit. 



isSetchell, Univ. Calif. Publ. Bot., vol. 5, pp. 1-86, 1912. 



