THK CANADIAN H( )RTIC^LTUK^^T. 



179- 



dew, or fog, or rain, it begins to swell, 

 the contents divide, and in an hour 

 and a quarter the segments resolve 

 themselves into oval bodies, which soon 

 rupture the wall of the spore and make 

 their escape, passing out slowly, usually 

 one at a time. Shortly after this each 

 of these oval bodies begins to move, 

 separates itself from its fellows, and at 

 length darts ofl" with great rapidity. 

 They are now called Zoospores, having 

 for about twenty minutes the power of 

 locomotion, at the end of that time 

 they cease to move, and in about 

 fifteen minutes after, an outgrowth 

 appears on one side, which de\'elops 

 into the mycelium of a new plant. The 

 usual number of zoospores that is pro- 

 duced from a conidium is five, each of 

 which becomes a new plant. The num- 

 ber of conidia that may be pi-oduced 

 from a single infested vine is to be 

 reckoned by millions, some computa- 

 tions going as high as ten millions, but 

 if we put it at five millions, and each of 

 these should find the conditions favora- 

 ble to reproduction, then we have to 

 multiply that five millions by five, so 

 that we have the almost incredible 

 number of twenty five millions as the 

 product of one infested grapevine. 



Fortunately the conditions are not 

 always present that favor the rejjroduc- 

 tive pi-ocess. Th<^re must alwa3^s be 

 the presence of water, else the conidia 

 cannot produce the zoospores ; and al- 

 though the process we have described 

 is not the only method of reproduction 

 that these wonderful plants possess, yet 

 in none of their modes of reproduction 

 can germination take place without the 

 presence of water. A moist atmos- 

 phere is not sufiicient. There must be 

 dro|)s of rain or dew upon the leaves, 

 or fruit, or growing branch into which 

 the conidia fall, in order to their further 

 development. We now understand why 

 it is that this form of mildew is more 

 prevalent in wet weather. Mi-. Wil- 



liam Saunders, in the United States 

 Agricultural Report for I 861, describes 

 his method of availing himself of this 

 fact in order to prevent the attacks of 

 this mildew, which was, to place a cov- 

 ering over the trellis of sufficient width 

 to prevent the fogs, or dews, or rains, 

 from wetting the foliage. 



We have already shewn that the ve- 

 getative portion of the fungus, called 

 the mycelium, grows within the tissues 

 of its host, hence it is impossible to de- 

 stroy the plant in that stage without 

 destroying the leaf also, or the fruit, if 

 the fungus be growing in the fruit. 

 Our hope is to find some means of pre- 

 venting the conidia from performing 

 their office of producing the zoospores, 

 from which the new plants ai-e deve- 

 loped. ]\Ir. Saunders' method may do 

 in small vineyards, but is difficult of 

 application to large establishments. 



The remedies that have been found 

 serviceable in Europe will now be enu- 

 merated, in the hope that they will be 

 carefully tested during the present sea- 

 son, and their usefulness in our climate 

 definitely ascertained. If we shall be 

 able to combat this pest of our vine- 

 yards with some measui-e of success, we 

 shall have gained much toward the so- 

 lution of profitable grape culture in 

 Ontario. 



Sulphate of Copper, either alone or 

 in mixture, has been found efficacious 

 in destroying the germs of this fungus. 

 The following preparations haye been 

 recommended for trial bv the United 

 States Commissioner of Agriculture. 



First — Spray the vines with a solu- 

 tion of 1 pound dissolved in 25 gallons 

 of water. 



Second — Dissolve a pound in 4- gal- 

 lons of warm water ; when completely 

 dissolved and the water has cooled, add 

 1 pint of commercial ammonia, and di- 

 lute this by adding 18 gallons of water, 

 and with this spray the vines. The 

 concentrated solution, that is, the four 



