AND ITS RELATION TO ANIMAL LIFE 147 



p. 264), which practical farmers know can be 

 killed by spraying with a solution of sulphate 

 of iron. The chemical action of this solution on 

 a plant would be towards producing chloro- 

 phyll, and as the dodders contain no chloro- 

 phyll, the chemical change produced would 

 be inimical to their growth ; in other words, the 

 iron acts as a poison to them. This chlorosis 

 being a common disease among the higher 

 plants, the presence of the parasitic dodder 

 may be taken as an indication of the chlorotic 

 state, for the conditions which will cure 

 chlorosis will kill the dodder. In other words, 

 when the soil is of such a nature as to produce 

 chlorophyll in the plant, the dodders, and, as 

 I believe, many other weeds will not thrive 

 in it. It has been shown by practical experi- 

 ment, sometimes made accidentally at great 

 cost, as in the case of destroying a whole 

 orange grove, that if you give plants too 

 much phosphates, potash and nitrogen, you 

 will kill them, and knowing that many soils 

 are very deficient, if not entirely wanting, in 

 iron, in which soils I feel sure it will be found 

 such weeds as the dodders, charlock, Canadian 

 thistle, and an innumerable number of other 



