MICROSCOPE AND AGRICULTURE 



burden. Very many cluster cups are known and 

 very many rusts and all that is required is an 

 enthusiastic mycologist, as the student of fungi is 

 called, to put the pieces of the puzzle together, so 

 to speak. It is not so very many years ago that 

 the connection between the cluster cups of barberry 

 and the rust of wheat was quite unthought of. 



We cannot afford much more space to plant 

 diseases, the farmer has other troubles and we must 

 mention some of them. We cannot leave the sub- 

 ject, however, without a word concerning the mil- 

 dews. As we have mentioned, they are curious 

 because they dwell outside the plants they attack. 

 Rose mildew is unfortunately all too common in 

 every garden, it may be recognised as a white 

 powder covering leaves and buds. Under the micro- 

 scope, in the summer we shall find that it consists 

 of a number of thread-like structures, not unlike 

 those of the common white mould and that there 

 are a number of erect chains of spores. Towards 

 autumn, a further examination will show us many 

 round dark-brown structures from which project a 

 number of minute threads. These brown spheres 

 are the winter stage of the fungus, designed to with- 

 stand inclement weather. In the spring, the spheres 

 burst and set free a number of minute sacs, each 

 one containing eight spores. The spores germinate 

 on rose leaves and start the disease anew. 



There will be no difficulty in finding mildews; 

 they are all very similar to the rose mildew in 

 general but they all differ in detail. The gooseberry 



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