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very destructive to fruits of all kinds ; and one species 

 commits great ravages on peach-trees, peas, and cabbages. 

 The Mane de rosier, which infests rose-bushes, is also an 

 ally of this, destructive corps. The year 1854 proved 

 most disastrous to the hop-growers in many districts, 

 owing to the ravages of an oidium. The lover of fruit 

 may have often noticed thin concentric, cream-coloured, 

 or fawn-coloured patches on the skin of apples, pears, 

 and plums, producing very rapid decay. These patches 

 are caused by Oidium fructigenum, which, when it has 

 once obtained possession of a tree, spreads with fatal 

 rapidity, destroying the fruit while still hanging on the 

 branches. 



All the mildews and blights hitherto described are 

 light-coloured ; but there is another class of fungi equally 

 destructive, called black mildews. They are caused 

 principally by species of Antennaria and allied genera, 

 which form thick, black, felt-like patches on leaves, dis- 

 figuring trees, and injuring them fatally, by closing up 

 their pores, and preventing the free admission of the air ; 

 as also by depriving them of the full, direct light of the 

 sun. They are principally developed on those leaves 

 which had previously been covered with the honey-dew 

 of the aphides or plant-lice ; and as these little creatures 

 cluster together and impair the vitality of whole trees 

 and forests, it may easily be seen how extensive are the 

 ravages of the fungi, which are thus developed. In the 

 Azores the orange-groves have suffered dreadfully from 

 this cause ; while in Ceylon the coffee-plantations, and 

 in the south of Europe the olive-trees, have sustained of 

 late years immense damage from an unusual development 



