'20 Bordeaux Mixture anfl Plants 



What the physiological effect of the absorbed copper may be is at 

 present uncertain. In a set of practical spraying experiments it was 

 noticed that in all cases (as has often been recorded) the colour of 

 the sprayed plants differed from that of the unsprayed, being of a darker 

 and rather bluish-green shade. This was especially noticeable in plants 

 treated ^vith Burgundy (Soda-Bordeaux) mixture. A further point 

 was that the darker green colour was not confined to leaves coated 

 with the spray. New foliage which developed after the spraying, showed 

 the colour effect almost equally well. A comparison of sections of leaves 

 of treated and untreated plants showed that the colour change was 

 due mainly, if not entirely, to the difference in the nature or amount of 

 the chlorophyll in the mesophyll tissues. It was not possible to decide 

 positively, whether there was also a difference in the colour of the 

 cuticular epidermal waUs and of the hairs. 



A colour effect was also noticed in the case of the broad beans. 

 The foliage of the copper-containing plants was on the whole notice- 

 ably darker in colour, although considerable variation in this respect, 

 due partly at any rate to the conditions of the experiment, was met with. 

 In marked cases the tint of the green colour differed considerably from 

 that of the normal leaf green of a healthy bean plant, being of a distinctly 

 bluer or greyer character. Comparison of alcoholic extracts of chloro- 

 phyll from copper-containing and copper-free foliage by spectroscopic 

 examination and other methods failed to reveal any difference between 

 the two ; and the colour of the extracts, unlike that of the leaves them- 

 selves, w^as practically identical. In making the chlorophyll extract, 

 however, it was noticed that in the case of the copper-containing foliage 

 there was considerable difficulty in obtaining complete extraction of 

 the colouring matter ; and generally after extraction the tissues instead 

 of being quite colourless, contained areas of a pale purplish-black tint. 

 Sections of the tissues showed that this colour was due not so much to 

 colouring matter within the cells as to cell walls stained with this tint. 

 The question of the influence of the copper in potato and other 

 foliage on the power of resistance of the plant to fungoid attack is still 

 under investigation. 



The results of these observations on foliage injury and tlie absorption 

 of copper by the plant from Bordeaux mixtures may be summarised as 

 follows : 



(1) Cells with readily permeable walls (such as germ tubes of fungus 

 spores, root hairs, the interior tissues of leaves, etc.) exert a considerable 



