No. 4.] PLANT DISEASES. 45 



Professor Jones. I am extremely interested in what Pro- 

 fessor Brooks has said. It is a subject of fundamental im- 

 portance, which deserves careful experimental study. In 

 Germany, Great Britain and France considerable attention 

 has been given to this matter of the relation of chemicals 

 to disease. They have not only come to rely on potash and 

 some other things as assistants to the disease resistance of 

 the potato plant, but they have come to guard against the 

 nitrogen as increasing the liability to disease. The potato 

 seed growers there are particular not to overfeed their plants 

 with nitrogen ; they say, if they do, the crop resulting from 

 that seed is more liable to disease. This has not, however, 

 been as fully demonstrated as it should be. Scotch grow- 

 ers, the best seed potato growers of Europe, wish to have 

 their seed " lifted," as they say, before it is ripe. They also 

 have a preference for seed not only from a certain type of 

 soil but of a certain size ; and they always wish it to be 

 northern grown, believing that to have superior disease- 

 resisting qualities. I believe we are only at the beginning 

 of the understanding of the relation of fertilizer, soil and 

 seed conditions to diseases of potatoes. 



Professor Brooks. There was one point that I didn't 

 speak of, which will take only a word to present. The pro- 

 fessor has told you of the presence of the green leaf-coloring 

 matter ; we find the potash salt has a marked effect upon 

 the coloring of the leaf. The shade of the leaf differs, show- 

 ing a different amount of colorino- matter. We find the use 

 of sulphates means more starch, and the use of chlorides 

 means less ; and, while we have no proof that there is a dif- 

 ferent eftect due to all the different potash salts, 3^et I rather 

 suspect we will find something of that sort later on. 



Mr. A. H. Smith (of West Springfield). It has occurred 

 to me, relative to Professor Brooks's statement, that grow- 

 ing plants to their most perfect form is the best insurance 

 that the ordinary farmer could have with reference to these 

 diseases and troubles. We have been raising a few acres of 

 potatoes yearly, and it has been my aim to get the land in 

 as good condition as possible for potato growing, to change 

 the plot yearly, and to dig the potatoes as early as the price 



