THE BROWN ROT OF SOLANACEAE : ENVIRONMENT 195 



Non-nutritional Environment. — Effect of heat, of sunlight, 

 of dry air (easily killed), of weak acids, of chloroform in bouillon, 

 of salted bouillons? 



What is the maximum temperature for growth? the mini- 

 mum temperature? the optimum? What is the effect of freez- 

 ing? Why does the organism so readily lose virulence (power 

 to infect) ? Can you discover any way to restore lost virulence? 

 Any convenient way to hasten its loss? 



There is reason to think that it sometimes dies out of soils 

 or is converted into an ordinary saprophyte (my own observa- 

 tions and those of Coleman in Mysore). If so, we ought to 

 be able to bring this about at will, thus disinfecting fields on 

 which certain crops cannot now be grown profitably on account 

 of its presence. Honing has found a soil-organism which is 

 harmful to it. Can you find any organism which, when sown 

 broadcast on a field, will destroy the parasite without injuring 

 the host? Cultural studies may eventually suggest the proper 

 treatment. 



For the disease. Signs. — Period of incubation. Time 

 required to infect the whole plant. Relative effect of few vs. 

 many punctures; of root vs. stem inoculations; of stem vs. leaf 

 inoculations; of inoculations on young vs. old plants. The 

 very susceptible tomato, Livingston's Dwarf Aristocrat, may 

 be used for this purpose, inoculating first when 3 inches high 

 and again when 2 feet high. On inoculated tomatoes how soon 

 do the leaves begin to bend downward? Where first, and how 

 soon, do the root-anlage appear on inoculated tomato shoots? 

 Where do they naturally appear later on uninoculated plants? 

 Can such root-anlage be made to develop further? Bind on 

 wet sphagnum or bury a portion of the stem without separating 

 it from the plant and examine from time to time. Have you 

 found any plant in which the disease occurs without the brown 

 stain? Are part of the signs due to a toxin? Inoculate 

 seedling Ricinus by needle-pricks at top of hypocotyl as the 

 plant emerges from the soil and compare subsequent growth 

 with that of control plants: there is a conspicuous dwarfing 

 due to such inoculations (Fig. 127). Consult also Fig. 131 and 

 try Helianthus annuus. Read what Hutchinson says about 



