2 PHYSIOLOGY OF THE FUNGI 



previous knowledge. Organization and interpretation of facts are equally 

 as important as the experimentation which reveals them. 



The fungi as a group are highly responsive to their environment and 

 are thus excellent test organisms for inquiring into the secrets of nature. 

 Nature always answers correctly the questions we ask, and, in this sense, 

 no experiment is a failure, although we may fail to ask the question we 

 intended, or we may misunderstand the answer given. Infinite care is 

 required to frame a question so that a definite answer may be obtained. 

 By observing fungi in nature we are limited to questions asked by nature. 

 Commonly, the environmental and nutritional factors are so complex that 

 the influence of a single variable cannot be evaluated. By controlling the 

 conditions under which a fungus is placed in the laboratory it is possible 

 to ask questions of great precision. Indeed, the number and scope of 

 the questions which we may ask fungi are limited only by the present-day 

 techniques and the curiosity of the investigator. 



Since most of our knowledge of the physiology of the fungi has been 

 gained from laboratory investigations, the experimental approach will 

 be emphasized in the discussions which follow. However, this choice is 

 not meant to minimize the importance of and need for critical observa- 

 tions in nature. By emphasizing the results of careful laboratory re- 

 search, we are better able in the following chapters to present the facts 

 necessary for an understanding of the vital principles of fungus physi- 

 ology, and also to show that these principles, theories, and hypotheses 

 are founded upon experimental evidence. 



FUNGUS PHYSIOLOGY IN RELATION TO OTHER SCIENCES 



Physiology is that branch of science which deals with the life processes or 

 the activities of organisms. The activities of the whole organism or of 

 any of its parts may be hmited by its form or structure. Both the 

 activity and the form of an individual are determined to a great extent 

 by its genetic constitution and are modified by the environment to which 

 the organism is exposed. Physiology, therefore, is not an independent 

 subject. An understanding of physiological principles is based, in part, 

 upon facts and theories from many other fields of science, such as chem- 

 istry, physics, anatomy, cytology, bacteriology, and genetics. 



Many of the physiological principles which have been established for 

 one group of organisms apply equally well to other groups. The vita- 

 mins essential to the normal growth of the fungi are the same as those 

 required by man, animals, and the higher plants. The general functions 

 of these vitamins appear to be the same in all organisms. The differ- 

 ence in the vitamin requirements seems to lie in the different abilities of 

 these groups of organisms (or individuals within the group) to synthesize 

 these necessary compounds. As Schopfer (1943) has pointed out, the 



