232 INSECTICIDES, FUNCrlCIDES, AND WEED KILLERS. 



a layer of bouillie bordelaise, give up to the water lying on them for 

 some time a quantity of dissolved copper capable of killing the spores 

 of fungi. When there is dew on a leaf, two liquids, separated by a 

 membrane, are present, the one is charged with soluble bodies, while 

 the other is pure water. It follows that exosmosis of the leaf may oc- 

 cur towards the dew. The organic substances thus in contact with the 

 deposit of cupric hydrate may dissolve not only the quantities required 

 to kill the germs fallen on the leaves, but also those indispensable to 

 the plant itself. Thus the dose of soluble copper collected in this way 

 by Clark killed the spirogyra. The water thus contained more than 

 -000001 per cent, an amount perfectly sufficient to stimulate the 

 jjlant. From the deadly effect of blue vitriol on the cells of plants, 

 and the difficulty with which this salt is absorbed, it does not neces- 

 sarily follow that the insoluble salts deposited on the plant behave in 

 the same way. Those which are insoluble and neutral would have 

 no action on the plant, nor on the spores of fungi, if they were not 

 rendered soluble and assimilable by conversion into a soluble organic salt, 

 which may be absorbed by the leaf and destroy the spores on the surface 

 of the organs of plants. The amounts of soluble copper salts required 

 to stimulate the plant are so small, and those which suffice to preserve 

 it from invasion, by injurious fungi, are so infinitesimal, that their 

 presence in the organs of the plant which have been in contact with 

 the copper cannot be chemically demonstrated ; but the principle of 

 absorption cannot be denied, since the constant presence of copper 

 in the ashes of the plants treated has been determined by analysis. 



Action of the Bouillie Bordelaise on Fresh=water Algae. — 

 Green alg£e behave towards copper like all green plants, but they are 

 much more sensitive to its action, probably because in the experiments 

 all the body of the plant dips into the poisonous solution. This plant 

 is perfect for allowing the observer to follow progressively the action 

 of blue vitriol on the living cell. Niigeli examined and determined 

 the precise action of blue vitriol on spirogyra. It was desired to de- 

 termine, likewise, how this alga behaves towards bouillie bordelaise. 

 Eumm undertook this work and examined separately the action of 

 the different ingredients composing bouillie bordelaise on the alga 

 Spirogyra longata. Sulphate of lime had no action. Calcium hydrate 

 is absorbed, beginning with a strength 1 in 3750 and then acts in an 

 injurious manner. Cupric hydrate is not sohible enough in water to 

 cede to it an amount of copper capable of preventing the growth of 

 the alga. On the other hand, the contact of cupric hydrate with the 

 alga kills it, owing to evident and visible absorption of copper. The 

 chlorophyll bands are torn, the plasma contracted, and the colour of 

 the contents browned. Eumm explains this fact by the secretions of 

 the alga dissolving the cupric hydrate, and the soluble derivatives ab- 

 sorbed by it of a certain sti^ength kill it. He observed, however, that 

 this action was more dilatory the more lime the bouillie bordelaise 

 contained. In presence of a large excess of lime the action became 

 nil. The bouillie bordelaise acts therefore on algie containing chloro- 

 phyll as on other green plants. 



Action of Bouillie Bordelaise on Fungi. — Cupric hydrate is 



