INTEODrCTION. 17 



treatment can thus be distinguished from preventive summer treat- 

 ment. Preventive winter treatment consists in destroying by chemical 

 agents all parasites, and the elements of their propagation. To obtain 

 this i-esult the trunks and branches are painted or washed, after a 

 mechanical dressing with milk of lime, concentrated copper bouillies, 

 10 per cent solutions of sulphuric acid, hot concentrated solutions of 

 sulphate of iron, boiling water, petroleum, and pure carbon disulphide. 

 These chemical agents, used in such a high degree of concentration, 

 do not injure the plant in winter, and permit of a radical destruction 

 of the parasites. These preventive winter treatments are, generally, 

 sufficient to prevent the diseases from appearing in the following year, 

 especially when care is taken to destroy the decayed organs scattered 

 around the plant, and to disinfect the soil, the dung, and the seed. 

 This last precaution is of an undoubted utility in preventing the 

 diseases of plants cropped annually, and the methods usually em- 

 ployed have now attained a great degree of perfection. Moreover, 

 it is necessary to destroy wild plants of the same species, which are 

 preferred by the parasites which it is desired to destroy, plants which 

 form seats of infection which are necessary to the cyclic development 

 of certain parasitic fungi, such as the rust of cereals, which search 

 for nurse plants of different species necessary for their normal evolu- 

 tion, and the destruction of which brings about the radical su]^;prcssion 

 of the parasite. These plants are the barberry and boragineae ("■■ p. 22). 



Preventive Summer Treatment. — In spite of preventive winter 

 treatments they must be completed by summer treatments. Working 

 so that the vulnerable organs of the plant are always protected by a 

 fungicide very slightly soluble in the dew, the plant is prevented 

 from succumbing to the incessant attacks of the spores, which the 

 atmospheric currents lead to it. It is a case of very small doses of 

 anticryptogamic agents, which suffice when the treatment is continued 

 during the whole period in which the disease is to be feared. Weak 

 injections of carbon disulphide in the soil and periodic washings of the 

 stock with dilute solutions of potassic sulpho-carbonate have given the 

 best results in the struggle against the phylloxera, without destroying 

 all the parasites they so far diminish their number that they can nO' 

 longer injure the plant. Sulphating every year with weak bouillies. 

 yields analogous results and enables the trees to develop normally. 

 Along with the rational and periodic use of chemical agents intended 

 to kill the greater part of the germs of cryptogamic diseases and insects, 

 it is well to use stimulants to furnish rational nutriment to the plants 

 and to pay attention to their hygiene. 



Hygienic Prophylaxy. — Vegetable therapeutics does not consist, 

 in fact, entirely in the struggle against the effective factors, but it 

 ought likewise to suppi'ess the adjuvant causes. Plants are restored 

 like animals by the art of healing regarded in its widest scope. Hygiene 

 which plays so great a role in human prophylaxy ought to receive 

 equal attention in the case of vegetables. This hygiene is based on 

 a knowledge of their organs, and their mode of growth, on that of the 

 environment where they live, and the climatic conditions which 

 favour their development, and the mineral elements indispensable to 



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