THE SCIENCE OF PLANT PATHOLOGY. 403 



the possibility of increased disease transference. Eecent years have 

 seen the San Jose scale spread from the Pacific to the Atlantic; the 

 asparagus rust from the Atlantic to the Pacific; the hollyhock rust 

 has invaded us from Europe ; the chrysanthemum rust from the Orient ; 

 the watermelon wilt is now moving northward and the peach yellows 

 southward. In nearly all cases where the soil is diseased the affected 

 region is annually enlarging, so that soil diseases a decade ago insig- 

 nificant in the territory of their occupation are fast assuming control 

 of alarmingly large regions. The growing of plants in larger quan- 

 tities also increases the amount of germ-bearing refuse to the ultimate 

 end that the very air and soil become germ laden. 



Civilization, higher culture and community life, especially if it 

 verge upon congestion of population, exacts an inevitable forfeiture 

 by increased mortality. Thus does the list of diseases that comes 

 within the horizon of the practical men enlarge. Wonder, often 

 skepticism, is expressed at the existence of unfamiliar diseases of man, 

 other animals and plants, as though these afflictions were conjured up 

 by the imagination of the over zealous practitioner. The increase of 

 affliction is more apparent than real, as it is in the case of appendicitis, 

 which is now recognized, named and cured, consequently, heard of, 

 whereas under the old regime it was not recognized as a distinct dis- 

 ease, therefore it was unheard of, though the patient died. Parallel 

 cases might be cited among the plants. 



The work of DeBary on polymorphism among the fungi is being 

 extended. Knowledge of the life histories of various pathogenic fungi 

 is being slowly expanded. Summer forms are connected with winter 

 forms, and thereby the hibernating condition, often the most vulnerable 

 point of attack, exposed. The discovery of heteroecism in the rusts, 

 the alternation from wheat to barberry, from apple to juniper is of 

 classic antiquity in the annals of plant pathology. It emphasized the 

 need of close study of life histories of all parasites. Such study has 

 given abundant fruit, notably in disclosing the relation between the 

 apple cankers and the ripe and bitter rot of the apple, and revealing 

 the winter condition of the brown rot of the peach. The lead so 

 fortunately made in the discovery of the Bordeaux mixture has been 

 assiduously prosecuted. The original Bordeaux mixture has been 

 greatly modified, changed, indeed, from a thick paste to a thin solu- 

 tion, and so thoroughly tested in all its modifications, that it has now 

 probably reached its ultimate perfection. Hundreds of other chem- 

 icals, both dry and wet, have been tested as fungicides, with the adop- 

 tion of a few adapted to special conditions, e. g., sulphur and sulphides 

 for powdery mildews and the ammoniacal copper carbonate for use 

 as the fruit ripens, thus avoiding unsightly spotting. A happy combi- 

 nation of insecticide and fungicide has been found in the various 



