32 Effect of Copper Compounds 



with that obtained by the application of Bordeaux mixture to the leaves. 

 If the quantity of copper introduced into the vegetable organism was 

 augmented, the toxic action of the metal began to come into play. 

 These investigators attributed the stimulus, as shown by the earlier 

 maturation of the fruits, to a greater activity of all the cells of the 

 organism and not to an excitation exercised only on the chlorophyll 

 functions. 



(b) Effect of solutions of copper salts on leaves. 



Treboux (1903) demonstrated the harmful action of solutions of 

 copper salts on leaves by means of experiments on shoots of Elodea 

 canadensis. The activity of photo-synthesis was measured by the rate 

 of emission of bubbles of oxygen. On placing the shoots first in water, 

 then in N/1, 000,000 copper sulphate ('0000159 %), there was a reduc- 

 tion from 20 to 15 or 16 bubbles in 5 minutes. On replacing in water 

 there was an increase to 18, but not to 20, indicating a permanent 

 injury. With ^/10,000,000 copper sulphate there was little or no reduc- 

 tion in the number of bubbles. This experiment had an interesting 

 side issue in that it was noticed that not only the concentration, but 

 also the quantity of fluid was concerned in the toxic action, indicating 

 that both the proportion and the actual amount of poison available 

 play their part. For instance, with a shoot 10 cm. long in 100 c.c. 

 solution the plants were only slightly affected by *000015/ copper 

 sulphate, but in 500 c.c. solution the shoots were killed after some 

 days in '0000015 / copper sulphate, a concentration only one-tenth 

 as great. 



While it is evident that copper sprays have a definite action upon 

 green leaves, whether favourable or unfavourable, the question arises as 

 to the means whereby the copper obtains access to the plant in order 

 to take effect. Dandeno found that solutions of copper sulphate were 

 absorbed by the leaves of Ampelopsis, forming a brown ring. Generally 

 speaking inorganic salts in solution are absorbed through both surfaces 

 of the leaves, whether the leaves are detached or not, provided the sur- 

 rounding atmospheric conditions are favourable, the absorption being 

 usually more ready through the lower surface. Dilute solutions applied 

 in drops stimulate the leaf tissue in a ring, whereas if the solutions are 

 concentrated the entire area covered by the drop is affected. Too con- 

 centrated solutions of copper sulphate applied to leaves caused scorch- 

 ing, but if this was avoided while the solution was still strong enough to 

 cause a darkening of green colour after a time, Dandeno considered that 



