SUPPLEMENT 57 



197, 1. 23 P. 198, 1. 13, for Oxalic acid . . . oxidized by the fungus read 

 Oxalic acid is especially frequently formed, and WEHMER'S (1891 and 1903) 

 exhaustive studies, as also those of BENECKE (1907), have made us fairly well 

 acquainted with the process. In the following account we shall followBENECKE's 

 summary in LAFAR'S Mykologie (I, p. 317). Among Mould Fungi Aspergillus 

 niger is known to produce oxalic acid vigorously, and it is on this fungus 

 that almost all the experiments have been carried out. The most important 

 result of these experiments is, perhaps, the discovery that the formation of 

 the acid is by no means an essential phenomenon, but that it occurs under 

 quite definite conditions. One might suppose that a deficiency in the supply 

 of oxygen must be the primary cause of ' incomplete respiration ' (as one 

 might term the process when oxalic acid appears in place of carbon-dioxide), 

 but that is not so, for the formation of oxalic acid is entirely independent of 

 the amount of oxygen supplied. The first factor concerned in its production 

 is temperature. At the optimum temperature (above 30 C.) the fungus pro- 

 duces oxalic acid just as at the ordinary temperature of a room, but it at once 

 carries the combustion of the acid which arises a step further ; by artificial 

 addition of oxalic acid, one may show that it is able to induce a more vigorous 

 oxidation at a temperature of that height. Further, by adding calcium car- 

 bonate one can induce an accumulation of the acid in the form of calcium 

 oxalate, and so prove that it is always of the nature of an intermediate product. 

 When cultivated at ordinary temperatures the fungus behaves according to 

 the composition of the nutritive solution in which it is grown. Should this 

 solution contain carbohydrate or salts of organic acids as the source of carbon, 

 a vigorous formation of free oxalic acid takes place, which, however, goes on 

 only until the solution has attained a certain degree of acidity, and this equili- 

 brium generally results when the solution contains about 0-3 per cent, oxalic 

 acid. When free acid is added to the culture, or after transformation of nutri- 

 ents into acid by the fungus, the production of free acid ceases. On the other 

 hand, the formation of free acid goes on uninterruptedly if substances cap- 

 able of combining with the acid (e.g. carbonates or alkaline phosphates) are 

 added, or if substances like these make their appearance as a result of the 

 metabolic processes in the fungus, as when ammonia appears after the addition 

 of peptone. WEHMER found that in one experiment Aspergillus formed 1-353 g- 

 of oxalic acid out of 1-5 g. of sugar when the acid was neutralized as soon as 

 formed. For this purpose, 0-8318 g. of sugar is used up, 0-290 g. being employed 

 for the construction of fungal substance, and 0-3782 g. oxidized into carbon- 

 dioxide. In a similar experiment with tartaric acid about half the amount of 

 oxalic acid possible was formed, while the free tartaric acid was completely 

 broken down into carbon-dioxide and water. In such an incomplete combustion 

 as that leading to the formation of oxalic acid, obviously the respiratory 

 material is not so fully made use of as when carbon-dioxide is formed, and 

 hence one may ask whether this imperfect utilization of products does not 

 make itself apparent in the growth of the fungus. The increase in dry weight 

 is, however, the same whether oxalic acid is formed or not, hence from the 

 nutritive and respiratory points of view the oxalic acid lost has no very great 

 value ; further, it is of no service as a source of carbon to the majority of 

 heterotrophic plants. On the other hand, the acid given off, in the free state, 

 has a very important biological significance, inasmuch as it acts as a poison 

 to other organisms. Oxalic acid is employed by many Fungi as a protective 

 weapon against other plants which, when dead, can then be made use of (DE 

 BARY, 1886). It serves also as a deterrent to other Fungi that live in similar 

 nutrient substrata (REINHARDT, 1892). It is of especial service when growth 

 of the fungus is inhibited by unsuitable temperatures, but the fungus can do 

 without it at optimal temperatures. 



