

been exposed to ver;- high or very low temperatures. '"it:. 

 a range of maintained temperatures extending about 12 degrees 

 or 15 degrees Cci.te 6 rade below a temperature sligntly above tne 

 optimum: temperature for enlargement, no influence of temperature 

 on structure was noticeable. 



Culture- Lth temperatures tnat approacned tne 

 maximum temperature foi enlargement snowed very different struc- 

 tures from tnose grown within the temperature range jU3t 

 Within tnis range favorable for enlargement the hyphae were oi 

 regular and simple form, mostly cylindrical, ai.d tne branching 

 wa3 regular. With temperatures x.ear tne maximum temperature for 

 enlargement the outgrowing hyphae were of irregular snapc, be: 

 and twieted, with occasional swellings and usually With apical 

 enlargements. Tne hyphal diameter was usually much largei than 

 witn more favorable temperatures for enlargement and tnese tnicter, 

 irregular hyphae showed ccnten s appeared dari. -colored a;. J gran- 

 ular, in contrast to tne smootn, clear appearanoe of tne cell 

 contents for cultures with tne more favorable temperatures. 

 The granulation was frequently pronounced and refraction was 

 such as to give tne whole hypha a very dense appearance. 



Typical visible differences between uypnae grown witn 

 temperatures near the maximum and tnose grown with temperatures 

 within tne optimal and sub-optimal range above mentioned, au 

 shown in figures 8 to 10. 



Tne drawings of figure 3 represent Phytophthora hyphae 

 near tne diSK margin. Tne regularly branched filament (a) 

 represents a culture grown 4 days with a maintained tempera- 

 ture of 33° C. Tne densely grandular and irregular filament (b) 

 represents a culture grown with a maintained temperature of 



32 



