383 



In the two experiments, the latex was coagulated to form sheet 

 rubber by the employment of 3 per cent, of its volume of 'formol'. 

 The rubber was kept for a quarter of an hour in water at 8o'C., then 

 passed through the press and well washed with water. The report of 

 the experts to which the samples were submitted showed that the 

 rubber had exactly the same appearance as that shown by Hevea 

 rubber from the Far East. It was valued at 2s. ^d. per lb., with Para 

 at 55. 10^. 



The wounds from tapping healed normally in the case of most of 

 the trees. With some, however, the bark dried up, and cracks were 

 produced in it, the wounds thus formed being attacked by insects. 



FUNGUS NOTES. 

 Recent Work on Bordeaux Mixture. 



In considering the poisonous action of copper salts on plant organ- 

 isms when they are used in the form of sprays, it must be borne in 

 mind that no substance in the solid form is capable of penetrating 

 the walls by which the living protoplasm of practically all plants is 

 protected, and that, consequently, in order to bring about the death of 

 the organism, the copper salt must be soluble in water. Such a soluble 

 salt is copper sulphate, or blue stone, and it might at first seem 

 that the application of a solution of this substance to diseased plants 

 would be all that is required to kill the fungi causing the disease. 

 This course has several drawbacks. In the first place, it is often found 

 that such a solution, when strong enough to kill the fungi, damages 

 the host plant as well ; secondly, it is easily washed off by rain. 



In order, therefore, to diminish its harmful effect on the host 

 plant, and at the same time to increase its adhesiveness, it is mixed, 

 in the preparation of Bordeaux mixture, with lime-water, or water 

 containing slaked lime partly in solution and partly in suspension. 

 As a result of this mixing, an insoluble compound of copper is 

 formed, which may often be mixed with excess of lime. The Bordeaux 

 mixture must contain no copper in the form of the soluble sulphate, 

 if injury to the leaves of the spra3^ed plant is to be avoided. Conse- 

 quently, enough lime is always added to turn all the copper into the 

 solid form. The liquid containing the insoluble copper precipitate 

 suspended in the form of fine particles is then sprayed on the plant, 

 and covers the parts to be protected with a fine film of insoluble cop- 

 per compounds. The question now naturall}'^ arises as to how this 

 insoluble substance is again rendered soluble, as it must be, if it is to 

 bring about the death of germinating fungus spores, which would 

 otherwise infect the sprayed plant. 



There are three theories which have been put forward to account 

 for the manner in which the insoluble copper compounds are rendered 

 soluble ; these are: (I) that the copper is brought into solution by the 



