146 PLANT DISEASE 



so that the two localities were hundreds of 

 miles apart. 



In order to show that the effect of the change 

 of soil upon the vegetation does not stop there, 

 it is important to note that the district in which 

 the above mentioned farmer lived is one in 

 which heart water is rife. He is one of the 

 very few who have noticed that a large per- 

 centage, if not all, the blood of an animal 

 suffering from heartwater would not coagu- 

 late, but sink into the ground like water. 



WEEDS, INSECTS AND MANURES 



For several years I have maintained that 

 many weeds owe their existence to an im- 

 poverished soil. I have noticed, for example, 

 that the presence of sorrel was always coinci- 

 dent with a deficiency of nitrogen, and have 

 found that after manuring with a nitrogenous 

 manure, the sorrel dwindled and died away. 



I have also noticed that when land was 

 limed on which Cape weed was growing, white 

 clover and other herbage grew to the exter- 

 mination of this weed. Again, there are the 

 dodders, parasitic plants containing no chloro- 

 phyll (see Encyclopaedia Britannica, vol. xviii., 



