326 



Notes on MildexVyfrom 



and, 3. Those which only attack the roots. All are ex- 

 tremely simple in their organisation, and very minute in their 

 forms ; they seldom appear but in autumn, except in forcing- 

 houses. 



The first class, or mildew composed of those fungi that 

 live on the surface of leaves, injure a plant by preventing its 

 respiration, but do not appear to draw any nourishment from 

 it. One of the most common of the fungi which attack the 

 common cabbage {^g. 85.) is Cylindrosporium concentricum 



Grev. These very destructive 

 fungi have the appearance of 

 small white patches, or specks, 

 of frosty incrustation, which, 

 when magnified, are found to 

 consist of a number of small 

 cylinders, lying end to end, or 

 across each other. These cylin- 

 ders are all filled with seed, and 

 burst when it is ripe, scattering it in every direction : wherever 

 it falls upon the leaf it takes root, and thus the fungus spreads 

 rapidly. The superficial mildew which attacks rose trees 

 and many other flowering shrubs is a kind of Uredo. This 

 name, derived from uro, Lat., to burn or 

 scorch, is applied to those occasional dis- 

 colorations of the surfaces of plants which 

 were formerly attributed to blights, or in- 

 juries from the atmosphere, and which 

 have the appearance of a brown powder. 

 Urhdo effijsa Gj^ev. {Jig. 86.) generally 

 shows itself on the under sides of the leaves 

 of the jRosacese, and spreads I'apidly. C/redo 

 Rosse Pers. is another kind, which also 

 attacks rose trees. The fungus called Acro- 

 sporium monilioides [Jig. 87.) consists of a 

 number of globules, attached to each other, 

 which, when magnified, appear like the 

 beads of a necklace, and in many cases are 

 upright. When ripe, these globules fall, 

 and, taking root, form fresh strings, or 

 necklaces, like the first. Sometimes little 

 tufts of these globules appear fixed to 

 stalks ; and, from some fancied resem- 

 blance to the brushes used for sprinkling 

 holy water, are called Aspergillus. {Jig. 88.) 

 The superficial mildew which infects the 

 onion, and is very fatal to that plant, is 



86 



found standing 



