182 Journal of A gricultural Research voi. xxi, No. 3 
The percentage of infections by Rhizoctonia solani was higher on the 
scratched series than in the previous experiments but no higher in the 
unscratched series. R. solani seems to require high humidity and a 
punctured epidermis to cause much infection and is, therefore, a weaker 
and more limited parasite on tomato than either Verticillium lycopersici 
or Macrosporium solani. Moreover, the infections caused by it were 
more superficial and usually disappeared as the plants became older. 
The infected areas produced by Macrosporium solani were usually a 
little darker in color than those made by Verticillium lycopersici or 
Rhizoctonia solani , especially on the older seedlings. 
.In order to determine whether the relative infectiousness of these 
fungi is the same in soil as when applied to the stems, sterilized soil was 
mixed with each culture, and in this were planted tomato seeds that had 
been treated with a solution of bichlorid of mercury i to 1,000 to destroy 
adhering parasites and had been washed in distilled water. The results 
obtained three weeks after this experiment was started are summarized 
in Table III. 
Table III .—Comparative infectiousness of collar-rot fungi in tomato seed bed 
.... . .Fungus. 
Number of 
plants 
grown. 
Number of 
plants af¬ 
fected by 
collar-rot. 
Percentage 
of plants 
affected by 
collar-rot. 
Verticillium lycopersici . 
567 
420 
362 
707 
64 
73 
Macrosporium solani .. 
Rhizoctonia solani .. 
O u / 
20 
0 
Control. 
/ DD 
282 
3 
A 
The results show that Verticillium lycopersici and Macrosporium 
solani produced nearly as high percentages of collar-rot infections as in 
the previous experiments in which the mycelium was placed directly 
in contact with the stem. Moreover, there was no distinguishable 
difference in the color or other appearance of the lesions produced by 
these two fungi. On the contrary, Rhizoctonia solani produced very 
few infections. In fact, under the conditions of this experiment it was 
not a very active parasite. 
The minimum growth temperatures obtained with cultures of these 
fungi were 1.5 0 C. for Macrosporium solani , 12 0 for Verticillium lyco¬ 
persici, and 15 0 for Rhizoctonia solani. In cold seed beds Macrosporium 
solani would, therefore, begin to grow before either of the other fungi 
but would have little advantage over them, as tomato seed will not 
usually germinate until it reaches a temperature of 14 0 or 15 0 . More¬ 
over, Macrosporium solani and Rhizoctonia solani grow and spread 
slowly while Verticillium lycopersici grows rapidly and spreads readily 
by means of innumerable spores. In seed bed or field it would there¬ 
fore probably spread much faster than either of the other fungi. 
