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JOURNAL 0¥ THE ROYAL HORTICULTURAL SOCIETY. 



produce conidia, and is reduced to its purely vegetative stage of a 

 filamentous mycelium. It is this new form which is particularly 

 dangerous, and which in propagating houses produces the rot which 

 causes such ravages among young seedlings and cuttings by inducing 

 decay. 



(c) Between the conidia stage and the sterile or filamentous one there 

 is a transitional phase, an intermediate form characterised by the simul- 

 taneous presence of mycelium filaments and a very few conidia. In this 

 condition the Botrytis is not quite harmless, but many plants can be 

 affected by it without serious damage. 



When the temperature is high and the air very humid this form appears 

 rapidly in vineries accompanied by the conidial type, which produces the 

 noble rot {'pourriture noble). It is frequent in damp temperate; houses 

 where the atmosphere is not confined. 



In a general way, according to M. Beauverie, this intermediate form is 

 produced in a very humid atmosphere at a temperature of 15° to 20° C. 

 If the thermometer rises to 30° C. the fungus assumes the barren fila- 

 mentous form unless the substratum be rich in nutritious matter for the 

 fungus. 



It is this intermediate form which has served M. Beauverie for his 

 immunising experiments. 



He obtained it by sowing B. cinerea spores on sterilised soil in Petri 

 boxes of large superficies. Maintaining these boxes at from 15° to 18° C. 

 the development of the attenuated type of Botrytis was very rapid, and 

 the soil was soon infected throughout. 



The contaminated soil was placed in ordinary pots which were then 

 filled with sowings and cuttings, especially Begonia cuttings. These 

 plants adapted themselves rapidly to the action of the attenuated form of 

 Botrytis, and being subsequently placed under conditions favourable to 

 the development of the filamentous or rot form this was abundantly 

 produced, but all the plants resisted its action. They were immune. 



It was necessary, however, to ascertain whether this immunity was 

 really the result of the treatment, or whether the resistance of the 

 vegetables under trial was simply due to a reduced virulence of the rot 

 developed under such conditions. 



The counter experiment was made, the " rot " form produced during 

 the trial was sown on the soil of plants not treated as above, and these 

 succumbed straightway. 



Doubt was no longer possible ; the immunity was certainly induced by 

 the treatment. 



It only remained now to determine a practical method of utilising the 

 discovery for the benefit of horticulture, and this M. Beauverie indicates 

 in a few words in the paper above cited, as presented by M. Gaston 

 B.mnier. According to this, in order to preserve seedlings and cuttings 

 from this form of rot it is sufficient to use soil infected by the inter- 

 mediate form of Botrytis cinerea. To do this the soil of a temperate 

 house sufficiently aired is sown with spores obtained from the conidial 

 form. The intermediate type develops very speedily. The sowings are 

 then made and cuttings are inserted in this soil, and then after a few 

 days' growth they can be carried into warm houses and submitted to 



