STIMULATION BY ASSOCIATIVE INTERACTION 291 



by either of the associated organisms acting alone. Molliard 

 (1903) first recorded the influence of one microorganism in stimu- 

 lating sporulation by another. He secured apothecia of Ascobolus 

 on carrot only when a bacterial contaminant was present. The 

 same sort of influence between species of fungi associated in the 

 same culture was first described by Heald and Pool ( 1908). They 

 secured an abundance of perithecia of Melanospora pampecma 

 grown in a mixture with Fasarhim moniliforme, Melanospora 

 ciilmorum, or Basispor'mm gallannn. Similar reactions occurred 

 if M. pampeana was planted on the media after these fungi had 

 grown on them and they had been sterilized. 



McCormick (1925) secured perithecia from monoconidial cul- 

 tures of Thielavia basicola, grown mixed with Cladosporhim ful- 

 vum, Aspergillus umbrosus, A. glaucus, Eurotium amstelodami, or 

 Fusicladmm pirinum. If aqueous extracts of these fungi were 

 passed through a Berkefeld filter, the filtrate retained its effective- 

 ness in stimulating perithecial production. Asthana and Hawker 

 (1936) got active stimulation of fruiting in Melanospora destruens 

 and other Ascomycetes by the addition to the culture medium of 

 the ether-insoluble fraction of nutrient solutions "staled" by 

 Fusarium, Botrytis, or Melanospora itself. Arrillaga (1935) noted 

 that the presence of Diaporthe citri stimulated the formation of 

 reproductive structures by Phytophthora citrophthora. 



Evidence of synergetic effects is not confined to responses in 

 cultures. It appears also to be manifest when a mixture of or- 

 ganisms is grown in tissues. Fawcett (1931) employed combina- 

 tions of several pathogens of citrus to inoculate into the bark of 

 citrus trees, with the result that lesions developed more rapidly 

 than when one organism alone comprised the inoculum. Fawcett 

 used in these experiments Diplodia natalensis, Colletotrichum 

 gloeosporioides, Diaporthe citri, Sphaceloma jawcetti, and Phy- 

 tophthora citrophthora. Savastano and Fawcett (1929) found 

 that Oospora citri-aurantii accelerated the rate of decay of citrus 

 fruits when, as inoculum, it was mixed with other organisms of 

 decay. 



More attention should be given to the synergetic reactions in- 

 volved in the production of lesions on plant parts. Once a lesion 

 has been initiated by the primary organism, it soon becomes in- 

 vaded by secondary organisms. These secondary species may 

 be found in some instances to play an important role in the pro- 



