Plants in their Relation to Disease. 167 



mensely wasteful, even alarmingly destructive. The precious stores of 

 fertility are exhausted by unprofitable combustion in the one case, and 

 swept off to the sea in the other. Let us not be content to sit at the feet 

 of Science ; but, inspired and equipped by the best knowledge of our day, 

 put into practice, with economy and intelligence, the best work of the world. 



PLANTS IN THEIR RELATION TO DISEASE. 



BY D. P. PENHALLOW, B. ?C., OF QUEBEC. 



In the year 1795 Schiiger brought together the very meager and scattered 

 literature relating to diseases of plants, and published it under the title of 

 " Empirical Directions for the Correct Determination of Diseases in Forest and 

 Garden Trees." This may be regarded as the beginning from which has since 

 developed the now very important branch of botanical science which specially 

 relates to disease, or vegetable pathology. At that time the science of botany 

 was hardly more than an infant, and the special department of vegetable 

 physiology was almost unknown. At that time also, the science of chemistry, 

 upon which correct pathological knowledge is very largely based, was just 

 entering upon a new era, and the more recently acquired facts were not 

 then available in their application to the laws of vegetable nutrition and 

 growth. It was during the period extending from 1770 to 1800 that we 

 received from the hands of Priestly, Cavendish, Watt, and Lavoisier our first 

 definite knowledge concerning the composition of the atmosphere and of 

 water; and although these investigators instituted certain experiments to 

 demonstrate the relation of these bodies to vegetable growth, their efforts 

 were chiefly directed to the end of proving the eflect of plants upon the soil 

 and its various constituents. From this we will at once see how scanty and 

 very unsaiisfactory must have been the grand total of information in this 

 direction. Everything pointed to recognition of disease by mere external 

 peculiarities alone, nothing whatever being known of the actual sources of 

 plant food and the specific relation of the various elements to the physiolog- 

 ical processes of growth. Indeed, it was not until 1804 that special light was 

 thrown upon this point when De Saussure in his " Recherches sur la Vegeta- 

 tion," first demonstrated from the chemical analysis of wood ashes, that the 

 mineral constituents therein contained were derived from the soil, and that 

 the normal growth of the plant was therefore dependent upon a proper 

 supply of food from this source, an opinion which was soon strongly indorsed 

 by Sir Humphrey Davy upon the basis of actual feeding experiments. These 

 researches gave a new direction to eflort, and served to leaven the scientific 

 mind with an unseen and slowly-working, but none the less powerful im- 

 pulse, which was to make its influence felt in later years. 



Following Schiiger, no general work appeared until 1833, when Unger 

 published his work, since which time the literature of the subject has rapidly 



