58 Lectures on Bacteria. [§ vi. 



others by its vegetative process and its products. This must 

 always be kept in mind in judging of processes on the large 

 scale ; attention to it supplies the explanation of a number of 

 phenomena which are at first sight puzzling. 



The influence of other agencies besides those which have 

 been mentioned on the vegetation of Bacteria cannot in general 

 be disputed, but in the present state of our knowledge it is of so 

 subordinate importance, that a very short notice of it will be 

 sufficient on this occasion. The dependence of carbon-as- 

 similation upon the rays of light in the forms which contain 

 chlorophyll follows of necessity from what we know of the 

 function of chlorophyll. With respect to other effects of light 

 we have only some uncertain statements by Zopf on the pro- 

 bable promotion of the growth of Beggiatoa roseo-persicina by 

 illumination, and an investigation by Engelmann (29) into the 

 dependence on the rays of light of the movements of a form 

 which, though named Bacterium photometricum, is possibly, to 

 judge by the illustrations, not a Bacterium at all. Influence of 

 light has not been proved in the case of the majority of Bacteria. 

 The effects of electricity have been recently investigated by Cohn 

 and Mendelssohn (30), and may be gathered from their paper. 



The dependence on the conditions of vegetation which we 

 have been considering is true of all stages and phases of the 

 normal vegetative process, not excepting its first beginnings, the 

 germination of the spores. Of this it must be specially remarked 

 that it occurs, as far as is at present known, only in a nutrient 

 substratum favourable to the vegetation of the species. This 

 agrees with the corresponding behaviour of some spores of Fungi, 

 those for example of Mucorini. It does not agree with that of 

 most other spores or with the seeds of flowering plants, which 

 germinate, or at least can germinate, without nutrient substances, 

 provided they are supplied with water, oxygen, and the necessary 

 warmth. 



It has been already stated above on page 19, that in some 

 cases, as in Bacillus Amylobacter, spore-formation takes place 



