482 Forestry Quarterly 



by a comparison of which error was ehminated and plant protec- 

 tion established on a sure basis. It was a fortunate trend of the 

 scientific mind which led the old chemists to look into the nature 

 of natural objects and thus lay down the beginning of our know- 

 ledge of the composition of common things. It would be diffi- 

 cult indeed to explain the phenomena of plant growth if the great 

 discovery of the transfer and metabolism of food substances be- 

 tween the living plant and the earth and air had not been made. 

 However, with this great discovery, the chemical factors gov- 

 erning plant growth were not fully understood for many years 

 afterwards. Meanwhile, many false positions were necessarily 

 taken by the investigators of the time. Strange as it may seem 

 with our present-day familiarity with the cause of many plant 

 diseases, and the old investigators were not ignorant of para- 

 sitism, deterioration in plant growth was in no wise attributed to 

 parasitic fungi. In fact the more conspicuous forms commonly 

 met with in the forest were only associated with folk lore and 

 were despised objects from a scientific standpoint. With an im- 

 perfect knowledge of parasitism and nutrition, disease was ex- 

 plained by soil exhaustion, congestion of water in the soil, or ex- 

 cessive fertility. Such a diagnosis was correct in many cases, and 

 we now recognize numerous pathological conditions induced in 

 part or wholly by factors other than plants or animals. But every 

 diseased condition could not be so explained. Numerous forms 

 of fungi were recognized in field and forest, but the opinion 

 held regarding them was similar to that so often expressed in the 

 timber regions of today. They were not associated with any kind 

 of decay. It was impossible to believe that a tree could become 

 infected by a germinating spore coming from without, and it 

 was believed that the disease originated within the tree itself in 

 a kind of spontaneous generation from deteriorating materials. 

 It is evident that much had to be done in the study of the minute 

 structure of things before the rotting of wounds, the formation 

 of cankers, etc., could be understood. 



The discovery of plant physiologists that it is possible to de- 

 termine the chemical composition of plants by the synthetic 

 method of artificial cultures was destined to lend a new impetus 

 to the investigations of plant physiology. A knowledge of the 

 substances selected from the air and earth by plants in order to 

 attain their optimum development has been of far-reaching sig- 



