466 Report op the Mycologist op the 



To prevent a possible misunderstanding which may arise from 

 what has just been said it should be stated that the rust fungus 

 consists of two portions: (1) a vegetative portion consisting of 

 delicate colorless threads (mycelium) which are found only on 

 the interior of the plant; and (2), a reproductive portion com- 

 posed of the brown spores found in the pustules just beneath the 

 epidermis of the leaf. The spores are the " seeds " of the fungus 

 and not the fungus itself. 



A few florists are not yet fully convinced that it is impossible 

 for rust to arise spontaneously. There are a few diseases of 

 plants which may be produced by unfavorable conditions of 

 climate or soil or methods of culture. Such diseases are called 

 physiological diseases and are never contagious. But no disease 

 which is due to the destroying action of parasitic fungi or bac- 

 teria can ever be produced by any conditions of climate, soil or 

 culture whatever unless the specific germ of the disease comes 

 in contact with the plant; however, such conditions may accel- 

 erate the advance of the disease by being favorable to the devel- 

 opment of the parasite or by reducing the vitality of the host- 

 plant. Carnation rust is caused by the fungus, Uromyces caryo- 

 phylUnus, which is a plant as truly as is the carnation itself. No 

 carnation plant can become affected with rust unless it was 

 propagated from a cutting containing the rust-mycelium or else 

 comes in contact with rust spores. The theory of spontaneous 

 generation, once vigorously advocated, has been, during the 

 present century, so completely exploded that it is no longer up- 

 held by any scientist in good standing. 



Another popular error which should be corrected is the idea 

 that the rust found on weeds is the same as carnation rust. In 

 one case,* at least, this error has appeared in print. From con- 

 versation with florists I have learned that there are a good many 

 who do not understand this matter. A Long Island florist once 

 told me that he had discovered the source of the rust which waa 

 attacking his carnations. He conducted me to a patch of Can- 

 ada thistles affected with the rust, Puccinia suaveolcns, and point- 



* Hfttfu Id, T. D., Garden and Forest, 1SS4, Vol. VII., p. 17. 



