THE NUTRITION OF HETEROTROPHIC PLANTS 179 



DuCLAUx (1885, 1889) finds the following substances of special value to 

 Aspergillus: — i. dextrose; 2. cane sugar; 3. lactose; 4. mannite ; 5. 

 alcohol ; 6. acetic acid ; 7. tartaric acid ; 8. butyric acid. 



Laborde (1897) has compared Aspergillus with another fungus {Euroiiopsis 

 gayoni) and found that the latter was unable to make use of cane sugar and 

 tartaric acid, although it accepted lactic acid which was quite unsuitable for 

 Aspergillus. Finally Went (1901) obtained the following series for Monilia 

 siiophila : — carbohydrates, acetic acid, mannite, glycerine, lactic acid, malic 

 acid, ethyl-alcohol, ethyl acetate, tartaric acid ; a number of other acids are 

 poor nutrients, while formic and benzoic acids are of no use at all. [Certain 

 Bacteria are able to exist with the aid of the traces of volatile organic com- 

 pounds occurring in the air (Beijerinck, 1903). According to certain older 

 experiments of Elfving this is true also of many Fungi.] 



There is nothing to be gained by the citation of additional examples, since 

 a comparison of the results obtained by different authors is at present un- 

 fortunately not possible, seeing that certain factors, of which we shall speak 

 by and by, have not been studied with sufficient completeness. Thus, e. g. 

 the nutritive value of a certain carbonaceous substance may depend on the 

 age of the fungus, for it is not infrequently the case that during germination 

 more exacting demands are made on such substances than later on ; Aspergillus, 

 e.g., germinates very badly in the presence of lactose and mannite, whilst 

 a somewhat older plant thrives quite well in the presence of these bodies. 

 In the second place, the chemical reaction of the substratum has to be noted. 

 In this relation there is a noticeable difference between Fungi and Bacteria ; 

 the former prefer weak acid solutions, the latter weak alkaline. In both cases, 

 however, an excess of free acid as well as of free alkali inhibits development. 

 The quality of the nitrogenous material also has an influence on the nutritive 

 value of any particular carbon compound. Thus glucose is the best source of 

 carbon for Monilia sitophila when peptone is used as the source of the supply 

 of nitrogen ; but if aspartic acid be used instead of peptone, cane sugar is 

 found to be far more valuable than glucose (Went, 1901). As may be easily 

 understood the concentration of the nutritive solution is of importance, but 

 Fungi have a wonderful capacity for adapting themselves to high degrees of 

 concentration, as elsewhere occurs only in the case of germinating pollen- 

 grains (CoRRENS, 1889. [MoLiscH, 1893.]) The high osmotic activities of 

 concentrated sugar solutions were alluded to earlier. Fungi germinating 

 in such solutions must develop a much higher osmotic pressure than usually 

 occurs in plant-cells, otherwise plasmolysis would be induced. Eschenhagen 

 (1889), who carried out experiments on this subject in the Leipzig Institute, 

 obtained the following values for the maximum degree of concentration (in 

 weight per cent.) which ordinary Fungi could tolerate : — 



From these numbers we may calculate how great the pressure in the 

 interior of the cells must be, since the osmotic value of the cell-sap in a turgid 

 cell must always exceed that of the external solution. 



[Raciborski (1905) has obtained even greater values, for he has shown 

 that Aspergillus glaucus and a species of Torula could grow in concentrated 

 salt solution ; Torula germinated in a saturated solution of lithium chloride, 

 that is to say, in a fluid which gives the highest osmotic pressure of all 

 neutral salts.] 



The adaptation to high degrees of concentration is apparently in many 

 cases effected by the formation of unknown osmotically active bodies in the cell 



n 2 



