PHYSIOLOGY OF FUNGI 39 



respiration here. Such works as that of Kostyehev and Lyon (1927) and cur- 

 rent textbooks on general physiology may be consulted for further informa- 

 tion. However, one should clearly distinguish between oxidation and fermen- 

 tation phenomena. Space will not permit of a full discussion of this problem 

 here, but some practical suggestions will be given in connection with the 

 methods for the study of fermentation (see p. 62). In general, little atten- 

 tion need be given to a consideration of oxygen supply under the ordinary 

 conditions of culture (Kadisch 1933). It sometimes happens, however, that in 

 small, tightly plugged test tubes there may not be a sufficient amount of oxy- 

 gen present to support sexual reproduction. In some cases a sudden change 

 in oxygen pressure may stimulate reproduction, especially if applied along 

 with other changes in the environment. 



Temperatiu-e Requirements. — These vary greatly with the species, some of 

 which grow well only at body temperature while others will make good growth 

 at all temperatures between room temperature (20° C.) and body tempera- 

 ture (37.5° C). The earlier authors spent much time in search for an opti- 

 mum temperature, little realizing that a temperature may be optimum for 

 an organism under one set of conditions while far from optimum under 

 another set of conditions (Blackman 1906). Later studies considered the 

 effect of temperature on rate of growth and found that growth roughly 

 follows van 't Hoff's law of doubling the rate for every ten degrees of tem- 

 perature in the middle part of the temperature range, but with a rapid falling 

 off of rate after a certain critical point is reached. The limits of growth are 

 usually much wider than those of reproduction as Klebs postulated. In gen- 

 eral, spores are adapted to withstand higher and lower temperatures than 

 vegetative structures, and ordinarily, thick-walled spores are much more re- 

 sistant than thin-walled spores, while spores resulting from the sexual act are 

 more resistant than those of asexual origin. 



Influence of Light. — That light has strong morphogenic influence has long 

 been recognized from observations in nature (well summarized by Elfving 

 1890). Since some organisms develop reproductive organs only in response 

 to light stimuli, light may be of considerable importance in cultures. On the 

 other hand, many fungi seem to develop as well in the dark as in the light. 

 Elfving suggested that light acts as an inhibitor of organic synthesis and that 

 the closer the food available is to the constituents of the protoplasm, the less 

 action the light has. In most plants light, especially of shorter wave lengths, 

 tends to restrict vegetative growth. Many subsequent investigators have ex- 

 tended these early observations. Neidhart (1924) reports lethal action of 

 x-rays and radium in Sporotrichum and Ectotrichophyton gypseum. Nadson 

 & Phillippov (1925) report interesting effects of x-rays on sexuality in Muco- 

 raceae. Dome & White (1931) report differential action of x-rays in different 

 groups of fungi, while using the x-rays for therapeutic purposes. (See also 

 Liebesny, Wertheim & Scholz 1933.) 



