THE SCIENCE OF PLANT PATHOLOGY. 405 



quiring considerable accuracy of manipulation was thoroughly effective. 

 This method, if no easier were to be had, was well worth to practical 

 agriculture all that the experiment stations of the world have ever 

 cost. "Within only a few years, however, the Jensen treatment was 

 supplanted by the formalin treatment; a treatment so simple, inex- 

 pensive and effective that, save for minor improvements of detail, the 

 end seems to have been reached in the search for preventives for the 

 particular diseases to which the method applies. 



Growth of knowledge concerning bacterial diseases has occurred, 

 beginning with the pear blight which baffled all horticulture prior to 

 the assertion of its bacterial nature by Professor Burrill. The proof 

 that bacteria can and do cause plant diseases has been definitely ad- 

 duced, and a large number of such diseases have been recognized upon 

 many plants. Not only from the scientific side have these ailments 

 been studied, but from the practical as well, and preventive and palli- 

 ative measures have in many instances been found. 



The soil is often spoken of as the living earth. Not only may it 

 live, but it also partakes of those chief accompaniments of life, viz., 

 health, sickness and death. A healthy soil may, from an agricultural 

 point of view, be regarded as one capable of fulfilling all its vital 

 functions; a sick soil, one in which some such functions are impaired. 

 •Of only one class of soil sickness may I speak, namely, that which 

 results in producing sick plants by harboring pathogenic germs. The 

 cotton wilt, the Texas root rot, the watermelon, tobacco, tomato and 

 cabbage wilts, the cabbage club foot and the onion smut are conspicu- 

 ous examples of disease so propagated. Diseases of this type not only 

 destroy the crop, but they preclude the possibility of successful culture 

 of the plant in question, or of its close botanical relatives for many 

 years. Such foes to agriculture have completely destroyed the possi- 

 bility of tobacco growing on many farms otherwise eminently adapted 

 to this crop and ill adapted to any other, resulting in great depreciation 

 in the value of the land. This encroachment upon valuable soil will 

 proceed yearly, and with geometrically increasing rapidity, until means 

 of prevention are discovered, as they have now been in some instances, 

 and the method of prevention becomes common knowledge. Soil dis- 

 eases, the most dreaded of all dangers to the plant, are prevalent to 

 much greater extent in the south than in the north. One field is known 

 to exist in South Carolina upon which neither melons, cotton nor cow- 

 peas can be grown. It is conceivable that many other germs could 

 infest one and the same field, but no greater affliction concerning such 

 staple crops seems possible. 



Growth in popular appreciation of the importance of plant diseases 

 and of the value of remedial and prophylactic measures is perhaps the 

 most striking characteristic of plant pathology in the last twenty years. 



