OBSERVATIONS ON THE VINE MILDEW. 291 



some accidental circumstance or the mode of cultivation. What 

 seems to prove this is, that the disease has been more virulent in 

 white than in black grapes, and tliat the vineyards have been 

 spared while the trellises have suffered. 



I shall terminate these remarks by a final observation on the 

 mode of propagation of Oidium Tuckeri. Professor Brongniart 

 told me lately that some persons thought they had remarked that 

 the fungus appeared first in stoves where the vine is cultivated to 

 obtain early grapes, and that by degrees it was communicated to 

 the surrounding trellises. Tliis point of origin, if it were well 

 established, would militate strongly in favour of contagion, but 

 in truth it proves nothing. In fact, if the malady is endemic, if 

 it is connected with a particular condition of the vines, it is very 

 natural that those which are inclosed in stoves should be more 

 diseased than those which are in the open air, since their vegeta- 

 tion is earlier tlian tliat of the others. The fungus cannot be 

 developed at the same time on plants which are placed in very 

 different circumstances. I am well aware that it may be ob- 

 jected that tlie one prepares and preserves the elements of con- 

 tagion till the others are in a fit condition for being infected, 

 but why tlien this preference for white grapes, and repugnance 

 for those that are black ? In this case the vines whether staked 

 or on trellises should be diseased, and we see tlie malady rage 

 principally in vines attached to walls, or surrounded by inclo- 

 sures. There is then something in this question which belongs 

 evidently to aspect and cultivation. If contagion exists, the 

 malady cannot cease to prevail in stoves, and in vineyards it 

 ought to take place as well in the month of September as in the 

 month of June or July, which is exactly the contrary to what 

 really does take place. If, on the contrary, the vine itself is 

 affected in the first instance, we see the Oidium prevail as long as 

 the disease lasts. When the points which were diseased are 

 cicatrized or dry, it disappears naturally, and does not invest, as 

 it ought to do, the surrounding surfaces which are sound. The 

 moulds are great gluttons ; they are to vegetable what insects 

 are to animal substances. They do not abandon their prey, or 

 rather cease to vegetate except when there is nothing left to feed 

 upon. They could then be j^ropagated in the months of Sep- 

 tember and October, because at tliis time atmospheric momenta 

 are certainly as favourable for their development as in the 

 months of June or July. But they axe not propagated because 

 the vital conditions of the vines are not the same. 



Let us admit for the moment that Oidium Tuckeri grows in 

 stoves, and that it spreads from thence into the surroiuiding dis- 

 tricts. By what means ought we to attack it ? There is but 

 one. The focus of infection is known, it is necessary in conse- 



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