Feb. 16. 1920 Temperature Relations of Potato-Rot Fungi 



513 



The minimum temperature of growth and germination for the five 

 Fusaria and the two Verticillia lies either somewhat above or somewhat 

 below 5° C. Fusarium discolor var. sulphur eum formed a small amount 

 of visible growth at 5° on the sixth day, but neither growth nor germina- 

 tion could be seen at 1° after 7 days, although it was observed after 2 

 weeks. F. oxysporum did not grow and did not germinate at 5° even in 

 two weeks. The remaining fungi did not produce visible growth at 5° 

 in the first 7 days, but the germination was found to have taken place 



DIAMETER OP COLONIES IN MILLIMETERS. 



Fig. I. — Graph showing the rate of growth of Fusarium coeruleum on potato agar at different tempera- 

 tures. The growth made during the first 24 hours is marked here with a dotted line. It was very 

 indistinct because the fungus was not in high culture. 



when plates were examined under the microscope. The length of the 

 germ tubes, however, varied considerably with different organisms. This 

 difference was particularly significant in the two Verticillia; the spores 

 of the culture No. 426 produced only very short germ tubes, while the 

 spores of the culture No. 427 formed a fair weave of fungal threads. 

 Brooks and Cooley * report no germination with F. radicicola at 5° even 

 after the expiration of 10 days, but they made their studies with corn- 

 meal agar cultures and the results thus obtained may not be fully com- 

 parable with those here reported. 



' Brooks, Charles, and Cooley, J. S. temperature relations op apple-rot pungi. In Jour. Agr. 

 Research, v. 8, no. 4, p. 139-164, 23 fig-, 3 pl- 1917- 



