ANTAGONISM 281 



All who have studied microorganisms on artificial media have 

 noted evidence of this antagonism between the colonies of differ- 

 ent species. An explanation for this phenomenon was first sought 

 by Raulin in 1869 [D'Aeth (1939)1 in experiments involving the 

 growth of A. niger on liquid synthetic media. He removed the 

 mycelial mat by filtration at intervals of 3 days and determined the 

 amount of growth during each successive 3 -day period. Most 

 growth occurred in the first period, with less in each period there- 

 after. From these results it was concluded that growth-affecting 

 substances are excreted by A. niger and that they remain in the 

 filtrate. The reciprocal influence of the simultaneous production 

 of such substances upon paired organisms in the same culture was 

 first studied by Reinhart in 1892 [D'Aeth (1939)]. Since then 

 similar studies have been made by, among others, Zeller and 

 Schmitz (1919), Porter (1924), Sanford and Broadfoot (1931), 

 Endo (1931, 1932, 1932a), Weindling (1932), Broadfoot (1933), 

 and Arrillaga (1935). 



Porter (1924) used 80 species of fungi and bacteria grown in 

 pairs on corn-meal agar. The fungi employed included Penicil- 

 lium glaucum, P. italicum, Rhizopus nigricans, Fnsariiim lini, F. 

 culmonem, F. coeruleum, Gloeosporinm piperatum, Colleto- 

 trichum nigrum, C. lindemiithianum, and Helminthosporinm 

 sativum. He classified their interactions into five groups, four of 

 which are antagonistic, showing differences in degree of inhibitory 

 action as follows: 



1. One species overgrows and inhibits the other. 



2. Each member of the pair exerts a slight mutual inhibition. 



3. One of the pair grows close to but around the other. 



4. Mutual inhibition is exhibited at a considerable distance, and 

 the two remain separate. 



Endo (1931, 1932, 1932a) found that Hypochnns centrifugus, 

 H. sasakii, and Sclerotium oryzae-sativae, causing root-rot diseases 

 of rice, are indifferent to certain other fungi, and antagonism was 

 exhibited in other combinations. 



Broadfoot (1933) studied the interaction of 66 species of micro- 

 organisms, many of them bacteria, with special consideration to 

 their antagonisms toward Ophiobolns graminis. Among the fungi 

 that he found to be antagonistic to O. graminis are Ascochyta 

 graminis, Botrytis cinerea, Helminthosporium sativum, Lepto- 



