3l8 GENERAL PLANT PATHOLOGY 



this problem is not only of national, but of international and inter- 

 continental importance. These papers should be read by every 

 serious-minded student. 



Plant protection may be secured by the use of spraying materials.^ 

 The principal rules to be observed in their use are: (i) the poison em- 

 ployed must be sufficiently strong or concentrated to kill the parasite, 

 but not sufficiently powerful to injure the host; (2) it must be applied at 

 the right time, as suggested by a knowledge of the life history of the 

 fungus, or insect in question. Such sprays may, therefore, be divided 

 into two kinds, viz., insecticides and fungicides. Applications of these 

 to healthy plants serve to protect the plant from the attacks of its 

 fungous and insect enemies. Vast possibilities of controlling disease 

 have been opened up by the treatment of seeds with hot water and other 

 substances before the seeds are planted. 



iMcCuE, C. A.: Plant Protection. Bull. 97, Del. Coll. Agric. Exper. Stat. 

 June IS, 1912; Rees, Charles C. and Macfarlane, Wallace: A Bibliography of 

 Recent Literature Concerning Plant Disease Prevention. Univ. of 111.: Agric. 

 Exper. Stat., Circular 183, May, 1915. 



