NUTRITIVE VALUE OF DIFFERENT CARBON-COMPOUNDS 381 



at least, as for example is the case in PJiotobacterium pJiosphorescens and 

 P. Pfliigeri. P. luminosinn and P. indiaun on the other hand can grow 

 when supplied with peptone only (Beyerinck), as can Penicillium glaiecinn 

 and many other fungi, the growth of which, however, is markedly favoured 

 by a supply of carbohydrates. Various non-essential substances such as 

 certain of the ash-constituents may be assimilated when metabolism is 

 active, while many organic compounds such as oxalic acid * may be utilized, 

 although by themselves they do not form suitable food-material for the 

 plants concerned. 



Fungi are especially adapted for researches upon the nutritive value 

 of different organic compounds, and such organisms as nitro-bacteria 

 and sulphur-bacteria, which have very special requirements, may enable 

 some idea to be obtained as to the importance and character of special 

 partial-functions. It is possible that in a particular organism the final 

 stages of metabolism are always of the same character whatever the organic 

 food may be, for a given fungus retains the same characteristics and pro- 

 duces the same living proteids whether it is fed with sugar, asparagin, 

 or other carbon-compounds. When a number of organic substances are 

 at the plant's disposal, it is quite possible that one may be chiefly con- 

 sumed in respiration, and another used mainly in the synthesis of proteids, 

 but these are by no means to be regarded as specific respiratory, or 

 synthetic material, for under different conditions either may be used for 

 all purposes. 



The nutritive necessities differ widely according to the mode of life, 

 so that a substance highly nutritive to one plant may be of little or no 

 use to another even though it is readily absorbed, and hence it is impossible 

 to arrange different food-substances in a linear series of descending or 

 ascending nutritive value which shall apply to all plants. One plant 

 may be able to grow upon a large number of different substances, another 

 upon a few only, but even those plants which can be fed with very 

 simple carbon-compounds have not necessarily a wide range of possible 

 nutrient materials. This appears to be the case, however, with Peni- 

 cillium glaucnvi) which is almost completely omnivorous and can develop 

 slowly on formic acid or urea 2 , whereas Bacillus methylicus which nourishes 

 itself with formic acid or methyl-alcohol, and Mycoderma aceti which 

 grows best upon acetic acid and alcohol, have a comparatively restricted 

 range 3 . Similarly nitro-bacteria cannot be cultivated by supplying them 



1 Cf. Wehmer, Bot. Zeitung, 1891, p. 533 ; Pfeffer, Jahrb. f. wiss. Bot., 1895, Bd. xxvin, p. 212. 



2 Diakonow, Ber. d. Bot. Ges., 1887, p. 385 ; Wehmer, Bot. Zeitung, 1891, p. 326; Thiele, Die 

 Temperaturgrenzen d. Schimmelpilze, 1896, p. 10. 



3 B. methylicus: Loew, Centralbl. f. Bact., 1892, Bd. xir, p. 462. M. aceti: Beyerinck, 

 ibid., 1891, p. 291. 



