flattened end of a platinum needls and was then inverted and 

 placed centrally upon the surface of a new a^ar plate. The 

 petri dishes containing the agar were 10 cm. -in diameter ar.ri 



/ cm. desp ; each contained approximately 15 cc. cf 

 corn-meal agar which had been poured hot and allowed to solid- 

 ify before tne transfers were made, After inoculation, the 

 experimental cultures were divided into seven like groups, and 

 one of these r^oups were placed in each of the seven chambers 

 of the temperature-control apparatus. The cultures of any 

 p-iven species always occupied the same relative position in 

 all the chambers and in all the series. Tbia precaution was 

 observed so that any possible difference in the temperatures 

 between the upper and lower portions of the chamber would not 

 render the measurements of the different lots of the sa-rs 



spec:' =s incomparable. "But ouch differences in temperature 

 of different parts of any one of the seven chambers proved to 

 be slight (less than .5 C. between the top and bottom of a 

 chamber) . The cultures of Phthiacystis ci tronhthcra and 

 Ph y t o ph t h o j ra t en-est ria occupied a position on the rack in a 

 chamber, at nearly the same level as the bulb of the ther- 

 mometer from which the temperature records were taken. The 

 cultures of Rhomopsis citri were about 15 cm. below and those 

 °* Dip l opia natal ensi s about 15 cm. above the thermometer 

 bulb, in each case. 



OBSERVATIONS OH GROWTH. 

 As the hyphae grew out in all directions from the 

 center of the plate, a rounded mat or mycelial disk was formed 



