GROWTH 29 



be measured with ease and accuracy. This growth tube is illustrated in 

 Fig. 3. 



These authors (Ryan et al, 1943) found the rate of linear growth of 

 Ncurospora sitophila in such a growth tube to be constant for 200 hr. 

 The growth-tube method has been used to study the effect of temperature, 

 pH, vitamin content, and other variables upon Neurospora. These 

 special tubes have another advantage over Petri dishes in that cultures 

 are well protected from contamination. The same culture may be 

 exposed to a variety of environmental conditions such as hght and tem- 

 perature. These tubes have the disadvantage that it is more difficult to 

 remove mycelium or fruit bodies for examination. In addition, aeration 

 may be poor and become a limiting factor for some fungi. 



Fig. 3. Growth tube patterned after those described by Ryan, Beadle, and Tatum 

 {Am. Jour. Botany 30: 784-799, 1943) for measuring linear growth. 



Dry weight. By weighing the mycelium and spores produced, an 

 accurate and objective measure of growth is obtained. For precise work 

 it is the method of choice. Where any significant weight of spores is pro- 

 duced, either Gooch or Alundum crucibles may be used to collect both 

 mycelium and spores. For most purposes the mycelium may be filtered 

 from the culture medium by use of a finely woven cloth and then trans- 

 ferred to weighing bottles or small aluminum cups. The excess medium 

 should be removed by washing and pressing the mycelium, which is then 

 dried to constant weight at 80 to 100°C. After the mycelium is dry, it is 

 weighed on an analytical balance. It is usually sufficient to record the 

 weight to the nearest milligram. 



Some fungi make better growth and sporulate more readily on agar 

 than in liquid medium. It is desirable to have an objective measure of 

 growth of agar cultures. Fries (1943) and Day and Hervey (1946) have 

 obtained the dry weight of cultures grown on agar. This technique 

 should be more widely used. The mycelium is freed from agar by briefly 

 autoclaving the cultures, filtering off the mycelial mats, and washing with 



