MOULDS AND RUSTS. 



11 



and young shoots of flowering plants, often 

 causing great annoyance to the farmer. 

 The grape mildew is a familiar example. 

 When the leaves are attacked they show the 

 disorder in yellowish-brown patches on the 

 upper side, and soon after they become sere 

 and dead. The under surface of the leaf 

 will reveal to the searching eye the cause of 

 the trouble. There will be seen thin, frost- 

 like patches, as represented in Fig. 11. Un- 

 der the microscope, each of these patches is 

 seen to be made up of a 

 forest of such objects as 

 appear in Fig. 12. This 

 picture represents a grape 

 leaf cut across, the line 

 n m showing the upper 

 surface, and o j) the 

 lower surface of the leaf. 

 Among the cells of the 

 leaf the root-like threads 

 of the fungus, c c, are 

 searching for food. The 

 tree-like object above bears numerous globu- 

 lar buds, which drop off and act as spores 

 in reproducing the plant. These buds are 

 killed by the action of frost ; they are there- 

 fore often called ''summer spores." The 



Fig. 12. 



