BOUILLIE BOEDELAISE. 229 



exuded on the surface of the leaves. Whichever of the two cases 

 occurs, or both together, it will be seen that cupric hydrate mixed with 

 a large excess of lime will not have such a rapid action as in the 

 absence of lime, the latter having a great affinity for carbonic acid. 

 It also neutralizes organic acids, and in many cases, as the action of 

 the bouillie bordelaise cannot be retarded, to stop infection an excess 

 of lime should be avoided. An excess of lime delays the action of 

 bouillie bordelaise one to ten days, according to the amount of lime 

 used. Bouillie bordelaise, when well prepared, combines all the pro- 

 perties required in an anticryptogamic bouillie, and all the substances 

 added to increase its toxic action on spores or adherence to the leaves 

 are useless if it be conscientiously prepared and used immediately 

 afterwards. To popularize its use the trade has prepared powders, 

 having exactly the composition of a normal bouillie, which only require 

 mixing with water to produce a bouillie bordelaise. The greater 

 number of these powders yield bad bouillies ; they may undergo de- 

 compositions, rendering them unfit for the preparation of a proper 

 bouillie, and yield heterogeneous bouillies, in w^hich undissolved blue 

 vitriol is plastered up with a layer of sulphate of lime. Not only does 

 it become difficult to use them with the spraying machine, but they 

 have all the defects of badly made bouillies. If applied by the bellows 

 the same thing occurs on the leaf, the chemical reaction is incomplete, 

 the blue vitriol acts as such and causes burns. Nothing, therefore, can 

 replace a bouillie made on the spot by one's self, with the precautions 

 indicated above, and no similar preparation can be either so adherent 

 or so efficient. 



Action of Cupric Hydrate on Plants. — Insoluble copper salts 

 appear to be absorbed to as great an extent by the roots as by the aerial 

 organs of the plant, and cause poisoning. If the doses absorbed are in- 

 finitesimal no poisoning occurs. The copper salts then exert a salutary 

 stimulating effect. It was thus essential to find a salt of copper which in 

 contact with plants was only absorbed in infinitesimal doses, simultane- 

 ously stimulating the growth of the plant and destroying cryptogamic 

 •disease. It was found that cupric hydrate fulfilled these conditions 

 best and that bouillie bordelaise could practically fill that role. The 

 cupric hydrate deposit formed on the leaves is very adherent, insoluble 

 in water, and barely soluble in water containing dissolved carbonic 

 acid or carbonate of ammonia. It lets the plant absorb it in infinitesi- 

 mally small doses, w^hich might escape detection in analysis, but which 

 none the less exist since their presence in the leaf renders it so far 

 immune to cryptogamic diseases, and especially vigorous analogous to 

 the condition realized by spraying the soil with blue viti'iol. Leaves 

 of the potato plant treated with bouillie bordelaise become thicker and 

 more vigorous, the chlorophyll increases, assimilation is more active, 

 and the starch content of the tubers greater (Frank and Kruger). 

 •Galloway got the same results with fruit trees. Young plants sprayed 

 three to four times a year showed much more rapid growth, and pre- 

 served their leaves into the winter. It is very evident since this cupric 

 treatment gives to the leaf a great assimilative force, and that it pro- 

 longs this into the winter, the young tree will have grown more rapidly 



