Forest Sanitation 485 



portant results. The symbiotic relation between plants and cer- 

 tain species of fungi in which the green plant was found to be 

 greatly benefited in return for the protection afforded the lower 

 organism has thrown much light on the vexing problem of the 

 inter-relationship of plant life. 



So it is that the study of plant growth has received much at- 

 tention of late years and no one can tell into what direction future 

 investigation will lead. New questions are continually arising 

 concerning the action of bacteria in soil and in plant tissue, and 

 the old idea that bacteria had nothing whatever to do with plant 

 disease is disproved. It is interesting to remember the skepti- 

 cism with which the statement that bacteria are of importance in 

 plant disease was first received. Not until it was definitely 

 proven that pear blight and a number of other fruit and vege- 

 table diseases were found to be induced by bacteria was the 

 study of plant bacteriology^ established. The importance of the 

 higher parasitic fungi in deteriorating the forest crop is now 

 generally recognized and has developed into a highly specialized 

 branch of scientific forestry, the object and aim of which is to 

 determine the cause of the disease and introduce practical 

 methods of control. It is evident that little can be done in com- 

 bating a disease unless the complete life history of the organism 

 producing it is known, and often the nature of the disease to- 

 gether with other poorly understood conditions are such as to 

 preclude any definite step being taken in its control or eradica- 

 tion. This state of affairs may result from a too wide distribu- 

 tion of the disease or exhaustion and failure of all known 

 methods, or it too frequently happens through lack of interest 

 in the matter by the persons most concerned. 



Fortunately, however, there are a number of plant diseases that 

 come within the power of man to control or to completely eradi- 

 cate. As in animal pathology, the most successful treatment of 

 plant diseases, especially those of the forest, must, out of ne- 

 cessity, be conducted along prophylactic lines. The forester, in 

 planning his silvicultural projects, selects those positions where 

 the slope, soil and general climatic conditions are favorable for 

 the development of a particularly desired species. This species 

 successfully withstands the climatic environment. Some para- 

 sitic disease associated with it in other situations may not find 

 the factors suitable for its best development and it does not appear 



