44 



SOIL CONDITIONS AND PLANT GROWTH 



can be used with great effect as manures wherever there is any 

 deficiency of potash in the soil. 1 



Lithium salts, on the other hand, have a toxic action on plants. 

 Gaunersdorper's older experiments (100) have been confirmed by 

 J. A. Voelcker (290), who found that amounts of the chloride, sul- 

 phate, or nitrate, corresponding to '00375 P er cent, of the metal were 

 distinctly injurious to wheat ; smaller amounts, however, appeared to 

 cause an increased growth. 



Casium salts are less harmful (189, 290). 



Calcium is an essential plant food, the function of which was first 

 carefully studied by von Raumer (233), but has not yet been satis- 

 factorily cleared up. Nothing can be inferred from the fact that, like 

 potassium, it occurs more in the leaf than in the seed. It certainly 

 gives tone and vigour to the plant ; gypsum is used in alkali regions 

 to counteract the harmful effects of excessive amounts of saline matter 

 in the soil. It also appears to stimulate root production : if calcium 

 is withheld from water cultures the size of the root is much reduced. 



Its most remarkable effects are seen in water cultures. Curiously 

 enough, single salts of potassium, magnesium, sodium, etc., are toxic 

 to plants, while a mixture of salts is not. Calcium salts are by much 

 the most powerful reducers of this toxic effect. Thus Kearney and 

 Cameron (145) found that a root of Lupinus albus was just killed 

 when immersed in '00125 N magnesium sulphate solution (7 parts per 

 100,000), but the effect was modified by added salts, as shown in 

 Table XX.: 



TABLE XX. EFFECT ON VARIOUS SALTS IN REDUCING THE TOXICITY OF MgSO 4 . 

 KEARNEY AND CAMERON (145). 



Hansteen (see 214) found that the toxic effect of potassium salts 

 used singly was overcome even when so little lime was added that 



the ratio = Osterhout found (223) that Vancheria sessilis 



K 2 O 840. 

 lived for three weeks in distilled water, but was killed in a few minutes 



by -1- N NaCl, and in a few days by -oooi N NaCl ; yet the toxic effect 



1 See also a paper by B. Schulze, Beitrag zur Frage der Diingung mit Natronsalzen 

 (Landw. Versnchs-Stat., 1913, 79-80, 431). 



