BOUILLIE BOEDELAISE. 231 



vitality of the deciduous organs of the plant. Green vitriol, being 

 present in commercial blue vitriol to at least 2 per cent as an impurity, 

 it was imagined, first in America, then in Germany, that the strengthen- 

 ing effect produced by the bouillie was only due to this green vitriol, 

 for which reason Aderhold advised the use of a bouillie bordelaise of 

 the following composition : Blue vitriol 1"9 per cent, green vitriol 

 0-1 per cent, lime 2 per cent. Guocdenovic, who examined these 

 bouillies, found that they had not any greater stimulating action than 

 an ordinary bouillie of 2 per cent blue vitriol and 2 per cent lime. 

 The dose of green vitriol, required to produce an analogous physio- 

 logical effect to that produced by spraying with bouillie bordelaise is 

 0*5 per cent. The plant must also come in contact with the soluble 

 salt, the green vitriol, the hydrated oxide of iron deposited on the 

 leaves having produced no result, except as a 3 per cent bouillie. A 

 bouillie containing O'l per cent of green vitriol in an insoluble form, 

 cannot therefore act on the plant and strengthen the action of the 

 bouillie bordelaise, far less the impurities, which only bring 0-04 per 

 cent of hydrat:d oxide of iron in contact with the leaves. It must 

 therefore be admitted that blue vitriol acts in the same way as green 

 vitriol, but it is about ten times more active in much smaller doses. 

 Then comes the problem of the absorption of the copper by the leaves 

 when this product is deposited thereon in an insoluble form. Although 

 the increase of the chlorophyll may be easily determined, although 

 the action of the copper on the plant be undeniable, it is very difficult 

 to find in the leaf, in consequence of this treatment, abnormal quantities 

 of copper. It is thus owing to imperfections in our methods of an- 

 alysis that it is generally believed that copper is not absorbed by the 

 leaf. Sestini has, however, found more than normal amounts of 

 copper in vitriolized vines. Analyses of this sort are very difficult 

 and very delicate to make, for many reagents, even distilled water 

 itself, may contain the infinitesimal doses of copper sought for in the 

 plants. Nageli, from experiments he made on the alga spirogyra, 

 concluded that a plant which did not show any symptom of poison- 

 ing could not have absorbed copper, as the latter, absorbed by a 

 cell, kills it, and since the favourable action of copper is undeni- 

 able, it must act at a distance. These conclusions raise hypothetical 

 questions which we cannot discuss. It will be sufficient to point 

 out some facts which plead in favour of absorption, and which show 

 that the plant is perfectly capable of dissolving insoluble copper 

 derivatives deposited on the surface of the leaves, and of absorbing 

 them in minimum quantity. Barth was the first to express the 

 opinion, so disputed by Droop and Wortmann, that cupric hydrate 

 is dissolved by the exudations of the leaf. Clark has given consider- 

 able support to this hypothesis. Having observed that animal and 

 vegetable substances were capable of dissolving cupric hydrate, an ob- 

 servation which Swingle had already made as regards the secretions 

 of certain fungi, he concluded that certain organic compounds con- 

 tained in the juice of plants may dissolve cupric hydrate. To verify 

 this hypothesis he wrought on the leaves of the peach-tree, which are 

 the most ready to absorb copper. In fact, these leaves covered with 



