38 Effect of Zinc Compounds 



purple red colour. The following figures are given for the quantities 

 of zinc carbonate (ZnCO 3 ) in the ash of these two plants : 



Tussilago Farfara. 



Root Leaf-stalk Leaf-blade 



2-51 / 3-26 % 1-75 % 1-63 % 2'90 % 2-83 % ZnC0 3 



= 1-629 % 2-115 % 1-136 % 1-058 % 1-882 % 1-836 % ZnO. 



Polygonwm aviculare. 



Root Stem Leaves 



1-77% 1-93% 2-25% 2-86% 1-24% 1-49% ZnC0 3 



= 1-148% 1-252 / 1-46% 1-856% -804 % -967 % ZnO. 



Other analyses of plants from zinc soils as against controls from normal 

 soils indicated the high water and high ash content of the zinc plants, 

 though the dry matter was low, and it is suggested that the increase of 

 the ash may be connected with a stimulation caused by the zinc salts, 

 unless it is due to phosphoric-acid hunger, since the calamine soils con- 

 cerned are very deficient in phosphorus. 



Javillier (1908 c) corroborated the early statements of Risse as to 

 the presence of considerable quantities of zinc in certain species of 

 Viola, Thlaspi and Armeria, and also he cited a list of other plants in 

 which zinc occurs in some quantity. Javillier, however, is of opinion 

 that zinc oxide, like the oxides of iron and manganese, is very common 

 in plant ash, being present in all plant organs. Zinc is specially 

 abundant in Coniferae, where it is probably characteristic, as is the 

 presence of manganese in the ash and manno-cellulose in the wood. 

 The so-called " calamine " plants show great powers of accommodation to 

 large amounts of zinc. 



Klopsch (1908) analysed 17 species of plants grown on soil in the 

 vicinity of zinc works, and showed that the plants evidently absorb 

 small quantities of zinc from their surroundings. He also regarded zinc 

 as a normal constituent of certain plants. 



II. EFFECT OF ZINC ON THE GROWTH OF HIGHER PLANTS. 



1. Toxic effect. 

 (a) Toxic action of zinc salts alone in water cultures. 



In comparison with copper little work has been done with regard to 

 the action of soluble zinc salts alone on higher plants when grown in 

 water cultures. Freytag (1868) stated that zinc salts must be very 

 dilute if the plants are not to be harmed, and that for zinc sulphate the 

 concentrations must not be more than 200 mg. per litre (= 1/5000). 



