174 INSECTICIDES, FUNGICIDES, AND WEED KILLETJS. 



port iiijectioa-i of a 0'25-0'5 per cent solution of tlie same sul)staiice. 

 The injurious action of green vitriol depends greatly on the nature of 

 the plant to which it is applied. Aqueous plants very fond of water 

 are much more sensitive than plants not fond of water. Mosses, for 

 example, feel the action of green vitriol much more than cereals. 

 A strong dose of green vitriol has a specially injurious action on the 

 vital functions of the plant ; thus Mayer found that, used for grain crops, 

 it hindered the grain from forming in the ear. 



TABLE XXl.—Shoioin(] the Number of lb. of Green Vitriol u-hich Wheat, liye, 

 Barley, and Oats, resjjcctively, caii bear ^er 16C0 lb. of Soil. 



AVhilst barley is unable to form its grain if the dose of green vitriol 

 contained in the soil is above that given in Table XXI, oats resist 

 better. The injurious action of green vitriol is explained by the fact 

 that in presence of tannins and certain other analogous products it is 

 readily decomposed into insoluble organic compounds and sulphuric 

 acid. The latter causes at a certain concentration the corrosion of the 

 cellular tissue and disturbs the osmotic phenomena of the cell-walls. 

 Deherain and Grandeau in France, Wrightson, Griffiths, and Munro 

 in England, have shown that 60 kilogrammes per hectare Q cwt. per 

 acre) may always be used with advantage, whilst a dose of 250 kilo- 

 grammes per hectare (2 cwt. per acre) was often injurious. 



Action of Green Vitriol on Fungi.— Iron is not only necessary 

 to green plants, but a small quantity of this product would also seem 

 to be required by parasitic plants with no chlorophyll. The latter are, 

 however, more sensitive to green vitriol, which, like blue vitriol, is often 

 a violent poison for them. As to spores it has been shown that the 

 injurious action is connected with the penetration of the green vitriol 

 through the exterior membrane. If this penetration does not occur 

 the action is nil, if it occurs vitality is arrested. Iron like copper may 

 be found in the interior of the spores by means of certain reagents. 

 To determine if green vitriol has penetrated the spores, these, after 

 steeping in the green vitriol solution, are washed for fifteen minutes, 

 then they are placed in a bath of yellow or red prussiate of potash and 

 a little hydrochloric acid. If the iron has been absorbed the spore 

 becomes blue. Wuthrich found this absorption in all cases where the 

 spore was dead after immersion in vitriol. According to the experi- 

 ments made up to now on fungi, green vitriol acts identically with blue 

 vitriol, which, however, is the more energetic. Wuthrich concludes that 

 the doses of green vitriol and of blue vitriol which produce the same 

 action on the spores of different fungi are proportional to the chemical 

 equivalents of these salts, gx-een vitriol, these proportions preserved 

 being ten times weaker. 



The following are the amounts of green vitriol and blue vitriol 

 required to stop the growth of spores : — 



