HOW TO GROW GOOD CORN. 189 



dust or meal on the leaves and stems of the affected 

 plants. With the microscope we see that they are 

 beautifully-organized plants, having a kind of rootlet 

 (mycelium) or spawn entering the tissues of the 

 living plants on which they grow, and delicate pe- 

 dicels supporting spores at the externally visible por- 

 tion of the plant. The botrytis of the potato and 

 turnip, the erysiphe or oidium of the hop, vine, and 

 other plants, are only different forms of mildew, which 

 in some shape or another will be found on most 

 plants. That these attack living tissues is quite cer- 

 tain ; but in the case of the potato, the turnip, and 

 the vine, there is reason to believe that they result, 

 to a very considerable extent, from diseased action 

 in their tissues. Eor example : the botrytis of the 

 potato seems to attack a crop much over-cultivated, 

 on the approach of wet and cold nights after a pros- 

 perous growth in warm sunshine. So, the oidium 

 seems to us to be most abundant on renewed growth 

 after a season of dry weather. Again : mildew in 

 turnips is sure to follow that check which a long 

 season of dry weather brings after a prosperous and 

 vigorous growth. All these circumstances at least 

 show how these attacks are favoured by the condi- 

 tions which bring disease. So much, indeed, is this 

 the case, that we found, upon experimenting with 

 some cucumbers in a warm stove, that as long as we 

 regularly watered the plants and gave them the re- 

 quisite air, they kept healthy; but, by neglecting 

 these conditions for a few days, we- obtained mildew 

 with the greatest certainty. 



The remedies against mildew are — to obtain as 

 healthy a growth as possible, and to maintain this 



