KUNKEL: SPORULATION IN MACROSPORIUM SOLANI 311 



and upon the jimson-weed {Datura stramonium).'' By growing the 

 Macrosporiums obtained from these three hosts side by side in pure 

 culture it is easy to observe that they are by no means aHke. Not 

 only are they different culturally, but the spores they produce are 

 quite unlike morphologically. The spores of M. daturae have an 

 attenuated beak that is very much longer than the beak on the spores 

 of M. solarii or M. tomato. The beak on the spores of M. tomato is 

 finer than the beak on the spores of the other two species. The 

 mycelium of M. tomato is also finer than the mycelium of the other 

 two forms. The spores of M. daturae are larger and the spores of M. 

 tomato are smaller than those of M. solani. On such media as string- 

 bean agar and glucose agar the three fungi show wide differences. 

 M. solani produces a gray felty growth on string-bean agar and 

 usually colors it red. No such color is to be observed in the case of 

 M. tomato and M. daturae on the same substratum. The growth of 

 M. solani on glucose agar is a rusty gray color. Colonies of M. 

 tomato and M. daturae on this same medium are blue in color. M. 

 daturae on many different media produces colonies showing marked 

 zonation, such as is not to be observed with the other two forms. 

 These three parasites are unlike in so many different ways that the 

 writer believes they should be considered separate species, rather 

 than strains of a single species. It is, of course, probable that either 

 fungus may infect more than one host. Sorauer (8) reports that he 

 was able to infect tomato leaves with the Macrosporium from the 

 potato. This does not prove, however, that the three hosts as they 

 grow in nature are attacked by one and the same fungus. An examina- 

 tion of the spores of the three fungi when grown side by side in wounded 

 cultures brings evidence that this is not the case. 



The method of obtaining abundant sporulation in cultures of M. 

 solani here described makes possible more extended infection-experi- 

 ments than have hitherto been undertaken. It is believed that it 

 will also be of service in any study of the systematic relationships of 

 the genus Macrosporium. The principle involved in the response of 

 the early blight fungus to a wound-stimulus is one well known to 

 science. Conditions unfavorable to vegetative growth often lead to 

 fruiting in unprolific plants. The orchardist recognizes this truth when 

 he prunes his trees or feeds them with fertilizers poor in nitrogen 

 compounds. 



BIBLIOGRAPHY 



I. Duggar, B. M. Fungous Diseases of Plants, (iinn and Co., New York, 1909. 

 2; Fries, E. Syst. Myc. 3: 373. 1829. 



3. Galloway, B. T. The Macrosporium Potato Disease. Agric. Science 7: 370- 

 382. 1893. 



