76 PLANT PHYSIOLOGY 



which green plants obtain from light, is in this case supplied by the oxidation 

 of this sulphate. 



Again, the methane-bacillus of SOHNGEN (1906) is also autotrophic. Large 

 quantities of carbon supplied in the methane are used up in the formation of 

 its cells, but whether the methane is first of all transformed into CO 2 , or 

 whether the methane is assimilated as such, is not known ; if the latter be the 

 case, then this organism might be regarded as autotrophic. In a flask con- 

 taining about 100 ccm. of pure mineral nutrients, 225 ccm. of methane were used 

 up in fourteen days, of which 126 ccm. were employed in the manufacture of 

 the Bacteria and 99 ccm. were transformed into CO 2 ; 149 ccm. of oxygen were 

 taken up in the process. 



Finally, as regards the Bacteria which oxidize hydrogen, investigations give 

 as yet very contradictory results. If we disregard the somewhat fantastic 

 statements of KASEKER (1906) and confine ourselves to NIKLEWSKI'S researches, 

 we find that these organisms which have not as yet been obtained pure are 

 without doubt capable of making use of CO 2 if they are able to oxidize hydrogen. 

 They differ, however, from the majority of autotrophic Bacteria in having the 

 power of becoming facultative heterotrophs. In a suitable nutrient medium 

 (acetates and also other less effective salts of organic acids) they can exist 

 without hydrogen ; the organic material then serves as well for the manufac- 

 ture of the substance of their bodies as for purposes of destructive metabolism. 



Under these circumstances one may conclude that the hydrogen Bacteria 

 practically never exist without respiring organic substance. With regard to the 

 majority of the other Bacteria discussed in this lecture, the question is still an 

 open one ; certainly in no case can ' normal respiration '- although it generally 

 takes place replace the oxidation of specific inorganic materials. It has been 

 definitely proved that respiration of organic substances does not, as a rule, 

 take place in thiosulphate Bacteria. Further, it follows that the living matter 

 itself does not suffer that continual destructive metabolism which would be 

 necessary to the maintenance of life (p. 204). 



231. Lecture XIX is XVIII of the 2nd German Edition. 



1. 36 P. 233, 1. 3, for DENITRIFICATION . . . activity of Bacteria. 

 read 



NITROGEN FIXATION. SYMBIOSIS AND METABIOSIS. 

 CIRCULATION OF CARBON AND NITROGEN 



In Lecture XVII we have seen that through the agency of micro-organisms 

 free nitrogen can be split off from nitric acid and from proteid. Since at an 

 earlier date no organisms capable of combining nitrogen were known, it was 

 thought that such continual loss of combined nitrogen must in the long run 

 render the existence of living things on the earth an impossibility (comp. 

 BUNCE, 1889). In reality, however, we have been long acquainted with the 

 fact that a measurable accumulation of combined nitrogen does take place 

 in certain arable soils, which could only have arisen from a combination of 

 nitrogen in the gaseous condition, and by the year 1892 BERTHELOT had 

 definitely shown that this combining of free nitrogen must be due to the 

 activity of Bacteria, since the process came to an end when the soil was 

 heated to a temperature of 100 C. It is to WINOGRADSKY that we owe the 

 first comprehensive studies on the behaviour of these Bacteria. 



233, 11. 41-3, for The isolation ... in vacuo. read The isolation of Clostridium 

 presented many and great difficulties, and was first successfully accomplished 

 when it was sown on carrots in vacuo. 



