•544 THE STINGING PROPERTY OF THE GIANT NETTLE-TREE, 



(c) By the concentration of the free acids in the stinging hairs 

 the plant is protected from certain natural enemies, such as 

 caterpillars, fungi, &c. 



(d) In the regulation of the chemical processes of metabolism 

 mass action plays an important part, as when the free formic and 

 acetic acids slowly liberate sulphuric, nitric (16), phosphoric acids, 

 etc., from their salts. These products, being assimilated by the 

 plant for the purpose of its complex proteid synthesis, are con- 

 tinually removed, so that the feeble chemical reactions may be 

 completed. 



(e) The inorganic constituents of the sap are present in 

 abnormally large quantities in the Nettle-Tree, and especially in 

 the leaves, where the active process of assimilation takes place. 

 Common forest trees like the oak and beech contain an average 

 of 4 to 5 % of ash in the dried leaves, and there is experimental 

 evidence to show that from 2 to 4 % only is absolutely necessary 

 to the plant; therefore all over this amount must be considered 

 as non-essential to the vital activity of the plant. 



Now in the Nettle-Tree we find 15-4 % of ash, and the presence 

 of this large amount can be explained by the excess of free acid 

 in the root sap exerting a powerful solvent action on the mineral 

 constituents of the soil. In this way the large amount of soluble 

 calcium salts finds its way to the leaves, and is there partly 

 deposited in an insoluble form in the epidermal cells. The free acid 

 is also able to convert calcium phosphate into the soluble phos- 

 phate, in which form we find it in the plant sap. 



Silica in the form of alkaline silicate, as shown by the analysis, 

 is carried up in solution from the soil, to provide material for the 

 cell walls of the hairs and the hard outer layer of the epidermis, 

 on which the silica is deposited in minute masses by chemical 

 precipitation, during the exchange by the alkali of silicate for 

 formate and acetate. 



In conclusion, after consideration of the various functions in 

 which organic acids take a part, we cannot believe that the 

 function of protection is the only one in this case. But the free 

 formate and acetate ions with the practically non-ionised acids 



