oct.8.i92i Temperature and Humidity Studies of Fusaria Rots 75 



control tubers were separated from the inoculated ones by a thin layer of 

 cotton. The entire apparatus was disinfected with formaldehyde gas 

 before the experiment was set up. 



The tubers used were of the Up-to-Date variety. They had been 

 kept over winter in a cool cellar, and a few sprouts which had started 

 were removed. They were inoculated by wounding the epidermis and 

 placing several drops of spore suspension in the wound. They were then 

 placed in the jars which were closed with cork tops and paraffined. The 

 inoculations were made with Fusarium oxysporum No. 8. The jars were 

 opened up and the tubers examined after five weeks. 



Set I (9° C). At 10 and 30 per cent humidity the tubers were all 

 healthy. 



At 70 per cent the tubers were sound with no penetration, although 

 there was a slight growth of mycelium on the surface of the tuber at the 

 point of inoculation. 



At 100 per cent the condition of tubers was the same as at 70 per cent, 

 except that the external growth of mycelium was greater. All the 

 control tubers of this set remained healthy, and both the controls and 

 inoculated tubers had sprouted. 



Set 2 (12.5° C). At 10 per cent humidity the tubers were healthy. 

 There was no invasion of the tissues. 



At 30 per cent, same as above with a slight external growth of mycelium 

 at the point of inoculation. 



At 70 per cent the tubers were about the same as at 30 per cent. 

 (PI. 10, A.) 



At 100 per cent invasion of the tissue had taken place for about 2 mm. 

 beyond the wound, causing a slight browning of the tissue. On the 

 surface there was a slight brown discoloration for several millimeters 

 surrounding the point of inoculation and a slight growth of aerial myce- 

 lium. All the control tubers in set 2 remained healthy, and both control 

 and inoculated tubers were sprouting normally. (PI. 10, B.) 



Set 3 (25° C). The control tubers remained healthy and sprouted 

 at 10 and 30 per cent relative humidity, while at 70 and 100 per cent 

 there was a slight disorganization of the tissue around the eyes and the 

 sprouts were all dead. No actual rotting was present or any fungus 

 growth. 



With infected tubers at 10 per cent humidity all inoculations were 

 successful and uniform. The fungus invaded the tissue for 2 cm. around 

 the wound. Immediately below the surface at the point of inoculation 

 there was in every case a cavity lined with a white mycelial growth. 

 The tissue surrounding the cavity was of a granular appearance. Exam- 

 ined under the microscope it appeared to be made up of a tangled mass of 

 mycelium and starch grains. A sof trot extended out from this area, the 

 tissue being light brown in color and completely invaded by mycelium 

 (PI. 10, C). 



