II. NOTES ON MISCELLANEOUS PLANT DISEASES. 



Macrosporium herculeum on Flat Turnips. 



Fig, 6, plate XXXII, is taken from a photograph of a flat-turnip 

 leaf affected with a spot of disease caused by the fungus Macro^-po- 

 rium herculeum E. & M. This disease of flat-turnips has been 

 common on Long Island during the past two seasons. In some 

 cases it has been so abundant as to seriously affect the growth 

 of the plants. 



Circular, dead, brittle spots appear on the leaf, which, if the 

 spots are numerous, withers and falls oft". If the upper surface 

 of one of the diseased spots is carefully scraped with a scalpel 

 and the scrapiugs examined with a comi)ouud microscope, nu- 

 merous brown, club-shaped spores will be found. (Fig. 1, 

 plate XXXII.) These are the spores of a species otMacrosporiuiii 

 which, upon comparison with authentic specimens, proves to be 

 31. herculeum E. & M. The species was oi'iginally described* on 

 horse-radish (Nasturtium armoracia), and so far as we know, has 

 never been reported as occurring on any other host. On Long 

 Island we have occasionally found it on cabbage leaves. On 

 both cabbage and turnip the gross characters of the fungus are 

 identical with those of Macrosporium cheiranthi Fr., var. 

 circinans B. & C, on these hosts, but the spores of the two species 

 are quite different. 



In a thin cross-section, made through a diseased spot, the 

 hyphae or feeding threads of the fungus *tnay easily be seen 

 traversing the tisues in every direction. 



There are many species of Macrosporium, the majority of which 

 are sappohytes. In damp weather they may be found on almost 

 any decaying vegetable matter. Often they take possession of 

 tissues which have been killed by other agencies, and so closely 

 simulate jtarasites that they are often mistaken for such, even 

 by expert mycologists; but there are a few species which are 

 certainly parasitic on plants. Af. herculeum is one of the un- 

 doubtedly parasitic species. 



* American Naturalist for Dec, 1883, p, lOOg. 



