40 Causes and Course of Organic Evolution 



base, and losing water and volatile products by evaporation 

 from its summit, while at the same time it absorbs and dis- 

 solves the gases of the atmosphere." So Leduc further adds: 

 "Like a living being, an osmotic growth absorbs nutriment 

 from the medium in which it grows, and this nutriment it 

 assimilates and organizes." 



With such phenomena before us it will be conceded as likely 

 that our knowledge of primitive organismal evolution will 

 best be advanced by study of those forms of life which consist 

 of simple and mostly non-nucleate cells. Further, if we learn 

 that these exhibit rather varied or even distinct modes of 

 vegetative existence, that conduce to perfect support and multi- 

 plication of the organisms, this will afford proof that not one, 

 but several and varied, modes of vegetative life-action were 

 primitively evolved. Thanks to the researches of Winogradsky, 

 of Nathansohn, of Beijerinck and others, we now know that 

 such truly proceeded. 



Some of the sulphur bacteria are quite colorless, or only 

 slightlj^ yellow from presence of glistening sulphur granules 

 in the tissue. As already stated, they can live in the dark, 

 while their supplies of energy are got from sulphur compounds. 

 The mode of nutrition of some of these may well be said to 

 confer on them the title of prototrophic, as suggested by A. 

 Fischer (39). Free hydrogen must often have been generated 

 during volcanic changes in the archsean period. This at 

 temperatures of 250° to 300° C. could unite with free sulphur 

 or ^dth sulphide salts to form hydrogen' sulphide, HgS. The 

 bacteria then absorb this into their colloid protoplasmic sub- 

 stance, and there oxidize it, setting free the sulphur in the 

 protoplasm as minute yellowish granules visible to the eye. 

 In the act of union of the hydrogen and oxygen, heat energy 

 is evolved. At the present day the earlier stages of the process 

 are started by the liberation of nascent hydrogen gas from 

 decomposing plants. This can readily unite with sulphate salts, 

 and by reduction action set free the hydrogen sulphide. 



So it may well be that we have, in existing sulphur bacteria 

 like Beggiatoa, Chromatium, and Thiotkrix, surviving types 



