XV 



STKUGGLE WITH DISEASE 



187 



This is an interesting little fact because it helps 

 to show us how all science, 

 that is all knowledge, is 

 linked together. We can- 

 not hope to learn every- 

 thing there is to know, we 

 cannot e.ven hope to be 

 interested in all know- 

 ledge, but it is wise to 

 learn to respect all know- 

 ledge, just because of this 

 fact that it has always 

 been found that one dis- 

 covery fits into another 

 like the pieces of a picture 

 puzzle. It is a very far FlG- 43 ._ A Section of a Potato 

 cry from mildew in wheat 

 to the discovery of the 

 aniline dyes, and yet 

 without the aid of those 

 dyes the botanists could 

 never have found out all 

 that they have found 

 about the minute plants 

 which produce mildew. 



Leaf, attacked by the fungus 

 which causes potato disease 

 (much magnified). a is the 

 under surface of the leaf, which 

 has pores (st.) through which 

 the fungus enters, b shows the 

 loose tissue of the leaf through 

 which the fungus threads (in) 

 spread. The spores (c) project 

 on stalks from the surface of 

 the leaf, and are carried by the 

 wind to other potato plants, so 

 that' the disease is very in- 

 fectious. 



Knowing also is the first 



step towards curing, and it is a big step. 



We have spoken of the ruin which such plant 



