134 BOARD OF AGRICULTURE. [Jan., 



and gardeners that many plant diseases, as, for example, the 

 rusts, smuts, mildews, and molds are caused by parasitic 

 fungi. We also know that some are caused by insects, as, 

 for e.xample, the leaf-spot of carnation called " stigmonose," 

 which results from puncturing the leaves by plant lice or by 

 mites; the root galls of some plants, which are caused by 

 eel worms, and those of others, which are caused by root lice. 

 Some diseased conditions of plants are also found which can- 

 not be attributed to any of the causes just named, but which re- 

 sult from what may be spoken of in a general way as unfavor- 

 able environment, as, for example, the tip burn of leaves of 

 lettuce, and other plants, and the dropsy of tomatoes in forc- 

 ing houses. Finally, there are some plant diseases, the cause 

 of which has not been determined. Peach yellows stands as 

 a prominent example of this class. 



Those who have had experience in growing plants, and 

 watching the progress and distribution of plant diseases, 

 know that the character of the season has much to do with 

 the prevalence of certain diseases. While it is true, for in- 

 stance, that the apple scab results from the attacks of a 

 parasitic fungus, it is very abundant in some seasons, while 

 in others it is but little in evidence. Likewise, the conditions 

 which prevail in certain locations favor the growth and spread 

 of the scab, while in other locations the prevailing conditions 

 are much less favorable to its development. Then, too, there 

 are certain varieties of the apple which are peculiarly sus- 

 ceptible to the attacks of the scab fungus, while other varieties 

 are comparatively immune. In all these characteristics apple 

 scab is typical of many other fungous diseases. We have, then, 

 in considering these diseases, first to know the nature of the 

 particular parasitic organism which may cause it, if it be due 

 to a parasitic organism, and, secondly, we need to study the 

 kind of diseases which are favored or retarded in their develop- 

 ment in many cases by the location. So that we can do a 

 great deal, therefore, by the selection of varieties, and by the 

 selection of locations favorable to these varieties, in com- 

 bating diseases. It is my purpose, however, to speak more 

 particularly of other lines of treatment, and to speak now of 

 the diseases which are caused by parasitic fungi. Great ad- 

 vances have been made in recent years in successfully and 

 economically treating fungous diseases. In order, however. 



