on or near the surface of the medium. This disk remained 

 practically circular, as it enlarged, for both Pyt hia cystis 

 ci tr ophthora and P>i onc o sis c i t r i , forming' a nearly perfect 

 circle at all stages of enlargement. The mycelial disks of 

 T)i p ic d i a. natal sn s is and Phytcphthora terreat ria were often 

 slightly irregular i^ form or evenly lohed, especially at the 

 h^her temperatures used. No irregularities ir growth such as 

 bring about zonation in mycelial mats of ^any funpi were o"' - 

 served in any of the maintained temperatures. In special 

 tests, however, i^ which the fungi were grown f o r a certain 

 time in cne tempera ,ture, and then transferred and grown in 

 a markedly different temperature, zonation was marked. 



Observations were made at daily intervals f o r a cul- 

 ture period of from four to six days on the enlargement of 

 each mycelial disks. The chief matter of observation was 

 the mean diameter of the disk, which was obtained by averaging 

 two measurements of different diametsrs, selected to represent 

 the disk as a whole. When the margin of the enlarginp disk 

 was clear and definite, these measurements were made by means 

 cf a thin millimeter scale applied on the bottom of the petri 

 disk, outside. Ir other cases the petri dishes were inverted 

 under a low power of a microscope and the length of the my- 

 celial outgrowth measured by means cf an ocular micrometer. 

 Measurements with a millimeter scale were read to within 

 .5 mm. This was deemed sufficiently precise for the purpose 

 since the differences between the rates of enlargement so 



SUpp uSol 



measured for cultures to be alike were often greater than this 

 amount. 



2£ 



