210 



IXSF.f'TICIDES, FrXGICIDES, AND WEED KILLERS. 



TABLE XXVI. — Showing the Effect of Solutions of Blue Vitriol of Variovs 

 Strengths on the Germination of Spores of Fungi. 



In 0"125 per cent solutions of blue vitriol the copper disappears in five 

 minutes' immersion, and is fixed on the spores. Spores of different 

 species of smuts behave differently from this point of view. 



Ustilago Panici-miliacei. — 0"5 gramme of spores absorbs all the 

 copper from 5 cubic centimetres of a solution of 0-125 per cent of blue 

 vitriol. 0-5 gramme of spores absorbs all the copper from 10 cubic 

 centimetres of a 0-125 per cent solution of blue vitriol. 0-5 gramme 

 of spores absorbs almost all the copper from 15 cubic centimetres of a 

 0125 per cent solution of blue vitriol. 



Ustilago Cramerl. — 0-5 gramme of spores absorbs all the copper 

 from 5 cubic centimetres of a 0-125 per cent solution of blue vitriol. 0-5 

 gramme of spores absorbs almost all the copper from 10 c.c. of a 

 solution of 0-125 per cent of blue vitriol. In the filtered liquid only- 

 sulphuric acid (dilute) remains. The spores treated by 5 per cent 

 hydrochloric acid cede the whole of their copper to this acid and re- 

 cover their original vitality. Blue vitriol acts, therefore, like formol, 

 by fixing itself on the chitinous membrane of the spores of fungi and 

 preventing their growth ; treated by an acid this compound disappears, 

 and the vital functions resume their natural course as before treatment 

 with blue vitriol. It is not therefore surprising that blue vitriol cannot 

 be detected in the interior of the cells by chemical reagents, since in 

 .small dose it does not penetrate but is retained on their surface. Al- 

 though blue vitriol in small doses does not kill spores it prevents their 

 normal evolution and the object sought is found. The plant is safe. 

 The dose of blue vitriol, therefore, required to prevent the growth of 

 spores is very small, and it is not difficult to produce this effect, since 

 by spraying with copper bouillies the plant is covered by a layer of a 

 slightly soluble co])pei' compound. 



Action of Blue Vitriol on Insects. — The larvae of insects with 

 a wet skin are as sensitive to blue vitriol as snails. The adult insects 

 may be poisoned by absorption from the leaves s])rayed with copper 

 co.npounds. The eggs of insects are much more insensitive to copper 

 salts than is generally believed, and to destroy them they require 

 steeping for a very long time in a strong solution of blue vitriol. 

 Penoncito has shown that the eggs of silk-worm {Bomhyx Mori) easily 

 resist a twenty-four hours' immersion in a bath of 1-2 per cent of blue 



