136 PROT1BCTION OF PLANTS 1923-24 



From a close study of the preceding table and growth diagrams, the fol- 

 lowing tentative conclusions may be drawn: 



1. The relationship between growth and H-ion concentration for the 

 six organisms was similar, that is, the growth of the fungus for a period of sixteen 

 days caused the solutions m which they grew to become less acid. On the 

 average the change was 1.1., and it is likely that had the cultures been conti- 

 nued for a longer period the change towards alkalinity would have been greater, 



2. From the fact that the triangulation diagrams showing best growth 

 are practically the same for all the organisms, it would appear that they are 

 identifical in their nutrient requirements. 



3. Since the best growth appears in the flasks nearest the apex of the 

 triangle KHo PO4 may be said to be the limiting factor for growth of the 

 three salts used. 



4. With the exception of the Saltation, there was a very marked similarity 

 in the tj^pe of growth. One organism could not be distinguished from another 

 at any time during the period of culturing. 



EflFect of light, temperature and carbon dioxide. 



As the result of numerous tests it was found that the temperature limits 

 for all the organisms were the same. 



Light was found to be responsible for zonation, high color and for a slight 

 retardation in the rate of growth. 



Experiments were carried out to ascertain whether the fungi would grow 

 in an atmosphere of carbon dioxide and if so whether any change in the type 

 of growth could be detected. It was found that the organisms growing in the 

 atmosphere of CO2 were exactly similar to the check cultures in every way. 

 The rate and type of growth were identical. 



Summary. 



1. Six organisms (Quebec organism, Saltation, Vermicularia varians, 

 Colleiotrichum tahHicum, Colletotrichum atramentarium, Colletotrichum atrovi- 

 rens) all causing a disease of the potato were used in these experiments. They 

 were grown on certain solid and liquid media. 



2. The following points were especially studied: 



(a) Type and rate of growth. 



(b) Salt requirement. 



(c) Hydrogen-ion reaction. 



(d) Morphological and physiological characteristics. 



(e) Effect of temperature, light and carbon dioxide. 



Conclusions. 



From the results of the above series of studies, the writer feels justified in 

 concluding that the Quebec organism, Vermicularia varians, Colletotrichum tabi- 

 ficum, Colletotrichum atramentarium and Colletotrichum atrovirens are identical 

 from a morphological and physiological standpoint. 



