13 



sulphate of coi)i;er (blue stone) or with one of the preparations in 

 which it is the important ingredient, known as Eau celeste, Bordeaux 

 mixture, etc. It seems very possible, too, that plants may be forti- 

 fied against the attacks of [):irasitic fungi, or their susceptibility to 

 such attacks be largely diminished, by special fertilization, for the 

 purpose of introducing into the plant substances which, while not 

 interfering with its growth, shall ma!<e it a less congenial soil for the 

 growth of fungi. The line of investigation here suggested, has not 

 yet been followed out, altliough it offers an opportunity for chemico- 

 physiological work which may yield important results. It is obvious, 

 also, that a vigorously healthy plant will resist the fatal influence of 

 parasites far better than a poorly nourished one. 



Much may be done, after a plant is too far gone to be saved; 

 to prevent further spread of the disease, by removing and 

 destroying the diseased parts. It is not sufficient, however, to tlirow 

 the portions removed into the rubbish heap ; the spores must be act- 

 ually destroyed and this can be effectually done only by burning. A 

 considerable number of fungi produce, in the plants on which they 

 live, resting-spores which ordinarily remain on or near the ground in 

 dead leaves or stubble, survive the winter, and, germinating in the 

 spring, infect the new growth. In these cases the danger of a severe 

 attack in the following year can be greatly lessened by clearing up 

 and burning all such sources of infection. 



Numerous instances can be cited of more or less common weeds 

 or wild plants so closely related to certain cultivated plants that they 

 are liable to the attacks of the same fungi, and so serve to perpetuate 

 those fungi and to infect the related cultivated plants when growing 

 near. Evidently, then, such plants should be carefully and thoroughly 

 exterminated wherever they may prove a source of danger. 



We may pass, now, to the application of the foregoing facts and 

 principles in the consideration of a few particular fungous diseases. 



THE BLACK-SPOT OF ROSE LEAVES. 

 Actinonema rosae Fr. 

 In December, 1887, my attention was called by Piof. S. T. May- 

 nard to a disease which considerably affected the leaves of roses 

 cultivated in the Durfee Plant House, and vs^hich he desired me to 

 investigate. The leaves presented all the external characters usual 

 to the disease which examination showed to exist, namely, the so-called 

 Black-Spot, caused by a parasitic fungus known as Actinonema rosae. 



