FUNGI. 21 



But fungi are not reproduced entirely by their spores. In a great 

 many eases, as I have mentioned before, the mycelium exists 

 perennially in the twigs and branches attacked, as well as in the 

 discarded fruit, and is capable of propagating the fungus under the 

 return of favorable conditions. In the former case the unsparing 

 use of the pruning-knife is the only reasonable cure. Familiar 

 examples of such perennial mycelium are the "black-knot" of 

 plum and cherry trees, in which case it is only necessary to watch 

 the growth of one of the " knots " from year to year to convince 

 yourselves that it renews itself annually from within the tissues of 

 the branch; the dreaded " anthracnose " of raspberries, grape 

 vines, etc.; also all of our more common "rust" fungi. 

 Only by cutting out and burning all diseased tissue, can such 

 diseases be eradicated. The destruction of wild plants which 

 harbor dangerous parasites is another point of hygienic importance. 

 Thus we can best protect our cherries from "black-knot" by 

 destroying neighboring wild cherry trees infected with the disease. 

 For reasons already explained the "rust" of apple trees may be 

 completely eradicated by the destruction of adjacent red cedars. 



Finally, most fungi require a considerable degree of moisture for 

 their most rapid development. An unusually warm, damp season 

 is accompanied by great fungous activity, and plants containing 

 much water are peculiarly liable to fungous attack. This is 

 perhaps more noticeable, and at the same time more readily 

 controlled, in the greenhouse than in the field. In such cases 

 thorough drainage, and the training of the plants so as to secure 

 thorough ventilation and the access of air and sunlight will do 

 more to prevent diseased conditions than any fungicide. 



I have dwelt thus extensively on the hygienic methods of pre- 

 venting disease, because I believe them to be of the utmost 

 importance, and deserving of far more attention than they usually 

 receive. I should, however, belie my own experience, did I not 

 emphasize the value of fungicides to supplement all hygienic 

 treatment. For convenience we may divide fungicides into three 

 classes — liquids, powders, and vapors. Of these the first and 

 second alone are adapted to field work, while the third is invalu- 

 able in the greenhouse or any enclosed space. Let us consider 

 first the liquids. 



As is well known, the salts of copper exercise, when applied in 

 sufl3cieut quantity, a most harmful effect upon all vegetation, the 



