8 



MASS. EXPERIMENT STATION BULLETIN 350 



favors rapid vegetative growth. Hasper (11) noted that several hours exposure 

 to direct sunlight is lethal to the spores. 



The influence of light on spore germination was considered by the writer in a 

 series of experiments. Fresh spores of the fungus were brushed on glass slides and 

 incubated in Petri dishes containing moist filter paper. One set of slides in each 

 experiment was placed in a black light-proof box; another set received only day- 

 light; and a third set was exposed throughout the total period of incubation to 

 artificial light of a 60-Watt Mazda daylight lamp, but far enough from it to 

 escape a lethal temperature influence. The details of the experiment and the 

 results are presented in Table 4. Continuous darkness was more favorable for 

 germination and growth than a combination of daylight and night darkness. 

 Light definitely retarded and suppressed spore germination and growth. 



Table 4. Effect of Light on Spore Germination and Growth in 

 Length of Germ Tube 



INFECTION PHENOMENA 

 Method of Infection 



Infection of the foliage and the green floral structures is entirely through 

 the stomata, and this manner of infection is believed to be due to a chemotactic 

 stimulus within the stomata exerted upon the germ tube (11, 13). Stomata are 

 present on both surfaces of the tomato leaf, but their numbers are much greater 

 on the lower surface. According to Small (29, 30), infection may occur on either 

 surface of the leaf, but inoculation of upper leaf surfaces produced leaf mold only 

 on the lower surfaces. Makemson (13) obtained successful infections on both 

 leaf surfaces but more on the lower surfaces. Caldis and Coons (5), using bits of 

 mycelium from pure culture, succeeded in infecting leaves only by inoculations 

 of the lower leaf surfaces. 



In the writer's experience, the fungus always dev^elops on the lower leaf surfaces 

 first, but in the later and final stages of the disease the upper leaf surfaces also 

 become densely covered with the fungus. Under natural conditions of inoculation 

 the older terminal leaflets are always the first to become infected, but according 



