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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 observations in nature.By emphasizing the results of careful laboratory research, we are better able in the following chapters to present the facts necessary for an understanding of the vital principles of fungus physiology, and also to show that these principles, theories, and hypotheses are founded upon experimental evidence. FUNGUS PHYSIOLOGY IN RELATION TO OTHER SCIENCESPhysiology 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 chemistry, 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 vitamins 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 difference 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 The life processes of the fungi involve numerous chemical transformations.Living organisms make and use special organic catalysts, enzymes, which control ...

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bined and dried at 100°C. to constant weight. Thus each figure given in the following tables, unless otherwise stated, represents the composite weight of five cultures. The actual weight of mycelium obtained under controlled conditions has been made the criterion for the evaluation of the comparative effectiveness of various factors. However, it should be emphasized that biological phenomena cannot be reduced to mathematical figures without making a generous allowance for the frequent and often disconcerting fluctuations that characterize the behavior of living things. No matter how rigidly one may control the environmental conditions and repeat a given experiment, one will always find some differences in the weight of the crop. Even the different cultures of the same experiment made at the same time and under identical conditions will continue to vary. We have found that such variations may be from 5 to 10 per cent; 'however, this is not great enough to be significant. P ART I. THE EFFECT OF THE AGAR FACTOR.-Allyn and Baldwin (1932) found that agar-agar exerted a decisive influence on the growth of certain bacteria. They ascribe this beneficial effect to the fact that agar is a mild reducing agent. The present writers (1938) observed that a number of fungi made better growth on solid media than on nutrient solutions and assumed that some chemical factor was the cause.The following experiments were made to test the effect of small amounts of agar upon the yield of mycelium of several organisms. The medium used consisted of 2.5 per cent dextrose, 0.3 per cent amino acids, the inorganic salts, and three concentrations of thiamin: 1/20th, 1/100th, and 1/500th ppm. One set of each solution received 0.05 per cent agar, while the other was without agar (table 1). Table 1 shows that the increase was greatest in the presence of 1/20th ppm. thiamin and that it disappeared in all cases except one when the vitamin was reduced to 1/500thppm. Thus, the yield of Ph,ycomyces blckesleeanus was increased by 84 per cent when thiamin was added at the rate of 1/20th TABLE 1. The effect of agar on the yield of mycelium in mg. b!/ five fungi.THE NECESSITY of an extraneous supply of thiamin for the growth of many fungi has been definitely established, but we know comparatively little concerning the influence of a number of contributory factors upon the growth of such organisms. The present investigation is an attempt to extend our knowledge concerning these factors. Part I of this paper concerns itself with the agar factor; Part II with the effect of organic acids upon nitrogen utilization; and Part III with nitrogen-dextrose-thiamin ratio.TECHNIQuE.-Unless otherwise stated, all cultures were grown on 25 ml. of nutrient solution in Erlenmeyer flasks of 250. ml. capacity. The basic medium consisted of 0.5 gram each of ammonium nitrate, potassium dihydrogen phosphate, magnesium sulfate, 5 grams of Bacto-Dextrose of highest purity, 0.5 gram of a mixture of amino acids (d-arginine, d-glutamic acid, l-aspartic acid, 2 parts each, and 1 pa...