22^ CAN LITIIIA BE A CONSTITUENT OF PLANT FOOD ? 



in considerable quantity without interfering with the normal 

 growth and development of plants. 



The two elements — lithium and caesium — the lightest and 

 the heaviest of the alkalies, are supposed to possess a destruc- 

 tive action on plant-life. Csesium has only once been found in 

 vegetable substance; Grandeau observed it in the ashes of beet- 

 root molasses. From the results of water-cultures and soil- 

 experiments, it appears that caesium compounds act as " a 

 poison on vegetable life." 



Litluum com]:)ounds are more widely distributed in soils, 

 and are also present in larger quantities in soils than csesium 

 compounds. Lithiimi has also been observed in a large number of 

 plants, such as Cardmis, Cirsiiiiii, Sdl'Z'ia, Saiiibitcus. and tobacco. 

 The ashes of Rhodesian tobacco, examined in the Chemical 

 Laboratory of the South African College, were also lithiferous, as 

 could easily be shewn by spectroscopic examination of the 

 ashes of the tobacco. It has been definitely proved that lithium 

 cannot displace potassium, and that it retards and even impedes 

 the growth of many plants, which had been planted or were 

 growing in soils and solutions, in which the potassium com- 

 pounds had been completely dis])laced b}' the corresponding 

 lithium compounds. 



In order to ascertain whether lithium compounds are 

 taken up by the roots together with potassium compounds, when 

 both kinds of compounds are present in solutions, and whether, 

 under these conditions, the seed of the plants grown contains 

 in addition to the potassium compounds also lithium compounds, 

 some water-culture experiments with wheat were carried out 

 in 1914 and 19x5. of which the following is a brief account. 



The two kinds of wheat Avere Spring JVJieat and Medeah 

 Wheat. 



The solutions contained, per litre : 



I gramme calcic nitrate. 

 .25 gramme magnesic sulphate. 

 .25 gramme potassic nitrate. 

 .25 gramme ferric phosphate. 

 .25 gramme hydric potassic phosphate. 

 .25 gramme lithic nitrate. 



Large, two-litre jars were used to give the roots ample 

 space for expansion. 



These experiments were started in June, 1914, and for the 

 first three months the solutions were changed weekly; subse- 

 quently on greater development fortnightly. 



Growth was well maintained till the end of September, when 

 all the plants showed signs of decline, and continued to do so. 

 In November the first signs of ears were seen. These developed 

 apparently in the usual manner. At the end of January all the 

 plants dried up. The " spring " wheat had then attained a 



