Effect of Copper Compounds 33 



the action was probably of the nature of a stimulus to growth, and pro- 

 duced a better development of chlorophyll and protoplasm in the region 

 where the tissues appeared dark to the naked eye, a conclusion which 

 tallies very closely with that of Frank and Kriiger. 



Amos (1907-8) experimented to see whether the application of 

 Bordeaux mixture affected the assimilation of carbon dioxide by the 

 leaves of plants, and whether any stimulation was produced. Brown 

 and Escombe's methods and apparatus were used and the summarised 

 results indicate that the application of Bordeaux mixture to the leaves 

 of plants diminishes the assimilation of carbon dioxide by those leaves 

 for a time. The effect gradually passes off, whatever the age of the 

 leaves may be. The suggestion is made that the stomata are blocked 

 by the Bordeaux mixture, so that less air diffuses into the intercellular 

 spaces and less carbon dioxide comes into contact with the absorptive 

 surfaces. If this hypothesis is correct, the physiological slackening of 

 assimilation is not due to the toxic action of the copper in the Bordeaux 

 mixture, but to a mechanical hindrance due to blocking of the stomata. 



III. EFFECT OF COPPER ON CERTAIN OF THE LOWER PLANTS. 



On turning to the lower plants, especially to some species of fungi, 

 one notices a striking contrast in their behaviour to that of the higher 

 plants. Some species of fungi have the power of living and flourishing 

 in the presence of relatively large quantities of copper compounds, or 

 even of copper or bronze in the solid state. Dubois (1890) found that 

 concentrated solutions of copper sulphate, neutralised by ammonia, which 

 were used for the immersion of gelatine plates used in photography, 

 showed white flocculent masses resembling the mycelium of Penicillium 

 and Aspergillus, which grew rapidly and fructified in Raulin's solution, 

 but which remained as mycelium in cupric solutions. The mould 

 proved capable of transforming copper sulphate into malachite in the 

 presence of a piece of bronze, but it was found that the presence of 

 the latter was not essential for the conversion into basic carbonate. 

 The same result was obtained if the culture liquid was put in contact 

 with a body which prevented it from becoming acid, fragments of 

 marble acting in this way. Copper sulphate solution in the presence 

 of the mould produced a green deposit on the marble, while without 

 the fungus the solution simply evaporated leaving a blue stain of 

 copper sulphate. 



B. 3 



