INTRODUCTION. 13 



generally used, and it is from it that the most successful results are to 

 be anticipated. 



External Treatment : Liquids. — Solutions, bouillies, emulsions 

 are much more used than gase'? and powders owing to their easy use. 

 These preparations are distributed by the spraying machine (figs. 8-12) 

 when the treatment is general, and by the brush when it is local. The 

 efficiency of the treatment by liquids depends to a great extent on the 

 mode of application. The substances should be projected in a finely 

 divided state, best in the form of a mist, because it is less important to 

 accumulate large quantities of substance in a given point than to 

 spread a little everywhere in a uniform manner, above as well as below 

 the leaves, on the twigs and on the trunks. The largest number of points 

 of contact between the spores of the fungi or the insect and the poisonous 

 solution must be secured. The appliances which attain this object 

 are the spraying machines which have reached a high degree of per- 

 fection. The liquid preparations must possess a certain degree of 

 concentration to be active. It is injurious to increase this concentra- 

 tion, and dangerous to diminish it. When a liquid preparation has a 

 poisonous action on the plant, or if it has no adherence, these draw- 

 backs may be obviated by multiplying the treatments with a weaker 

 preparation. It has been found that it is better to diminish the 

 strength of the applications and to increase the number of spray- 

 ings, for it is the abundance of these rather than the strength of 

 the preparation which forms on all the organs, in proportion as they 

 are developed, an extremely thin layer of a toxic substance capable 

 of preventing the development of spores or of poisoning parasites. 



Experience has proven that periodically spraying at short intervals 

 with weak bouillies yields far better results than a single annual 

 spraying with concentrated bouillie as formerly practised. The single 

 spraying with a 4 per cent copper sulphate bouillie used some years 

 ago has been replaced by three to seven treatments with bouillies 

 prepared with 0'5 per cent of copper sulphate. Although the total 

 amount of copper spread on the surface of the plant be mostly less 

 than formerly, the result is better, because all the surface of the plant 

 remains covered with a very thin pellicle of hydrated oxide of copper 

 of which a trace dissolved in rain water or dew suffices, as has been 

 found, to kill the spores which are germinated. This new process is 

 the more efficient because it especially guarantees against disease all 

 the young organs of the plant, which being more tender and more 

 aqueous, are more easily invaded by parasitic fungi and have there- 

 fore a greater receptivity for cryptogamic diseases. The perfection of 

 the treatment is, therefore, an element as important to secure success 

 as the properties of the product. When anti-cryptogamic substances 

 are used, it is necessary to bear in mind that the external treatment of 

 a plant cannot destroy the mycelium of the fungus which has penetrated 

 into the plant, and its multiple ramifications in the interior of the 

 latter are perfectly protected from all outside spraying. The ex- 

 ternal treatments are intended to destroy the organs that disseminate 

 the disease, the conidiophores and isolated spores, and thus prevent the 

 extension of the disease to other plants. If for any reason the treat- 



