Respiration of Phycomyces

No direct influence of light on respiration could be detected. Experiments were further carried out on the influence of other external factors on the respiration of Phycomyces Blakesleeanus. By means of an exact determination of the respiratory quotients it was possible to find what kind of food the fungus used from a heterogeneous culture medium. The grand period of respiration was determined at 25° C. on different quantities and different kinds of culture medium. The length of the sporangiophores is an index of their stage of development, corresponding to a specific point in the grand period. As a medium rich in oil I used ground linseed, as a starchmedium bread. The respiratory quotient varies in different parts of the grand period of respiration. On linseed it rises from about 0.65 to about 0.75. On bread it becomes 1.00 in the long run but at the maximum of respiration it is about 1.20. It was made probable that this is due to the manufacture of fat from carbohydrates. Phycomyces by preference takes fat when this is to be had; on fatty media the respiration is more intense than on starch-media. Proteins do not essentially participate in the respiration. The fungus cannot live anaerobically, neither on oil-media nor on carbohydrates. A decrease in oxygen tension affects Phycomyces very soon. On starch-media some effect becomes noticeable in about 9 per cent, of oxygen, in 2 per cent, of oxygen the respiration is reduced to half the normal amount. Phycomyces can stand low oxygen tensions on oil-media better than on carbohydrate media, at least in so far as the COa-evolution is concerned. On oil-media there is a visible influence in about 7 per cent, of oxygen, in 2 per cent, of oxygen the C02-evolution is reduced to about 70 per cent, of the normal amount. On bread the respiratory quotient does not change in smaller percentages of oxygen, it increases on linseed media. Pure oxygen has no influence on the C02-respiration, the 02-consumption only increases by a small amount. It was proved that respiration adapts itself at once to new temperatures and that a gradual adaptation to new temperatures as found by former investigators may be caused by experimental errors. At all temperatures the respiration can be represented by flowing lines, oscillations in the respiration did not occur. At harmful temperatures the consumption of fat changes into a consumption of carbohydrates. On linseed the ”zero-hour”-line has therefore a peculiar course. Both the ”Oa-curve” and the ”C02-curve” are slightly convex towards the temperature axis, at high harmful temperatures, the ”02- curve” becomes an optimum curve because the 02 values approach the C02 values and therefore decrease. The respiration on carbohydrate media is an almost linear function of the temperature. The "zero-hour” line deviates from the straight line at high temperatures. The foregoing investigations were carried out in the Botanical Laboratory of the University of Utrecht. This is the place to express my appreciation to Prof. Dr. F. A. F. C. Went for his kindly help, interest and criticism.