§ VI.] Vegetative processes. 



49 



VI. 



Vegetative processes. External conditions : tempera- 

 ture and material character of the environment. Prac- 

 tical application of these in cultures, in disiafection, 

 and in antisepsis. 



In passing on to the consideration of processes of vegetation, 

 we must first of all remember that agreement in structure and 

 development between Bacteria and other lower organisms neces- 

 sarily implies also an agreement in the chief phenomena and 

 chief conditions of vegetative life. In fact we have simply to 

 do with special cases of phenomena which are of general occur- 

 rence in all living organisms, and which do not differ more from 

 those to be met with in other plants than these do from one 

 another. It is specially true of the Bacteria which do not 

 contain chlorophyll, that their vegetative process agrees essen- 

 tially with that of other vegetable cells which do not contain 

 chlorophyll, both those which belong to the higher plants, and 

 more particularly those belonging to the Fungi. It is to the 

 investigation of the Fungi, which are more easily studied, that we 

 owe much of the advance that has been made in our knowledge 

 of the Bacteria. It is perhaps scarcely necessary to observe 

 that differences prevail from one case to another among Bacteria 

 also as regards the phenomena and conditions of vegetation, 

 analogous with those in the allied groups. 



Our present object, however, is not to give a complete account 

 of everything belonging to the vegetative process, but only to 

 call attention to the points most worthy of notice in connection 

 with the subject of these lectures. The conditions of tempera- 

 ture and the material character of the environment are chiefly 

 to be considered. 



Every process of vegetation is dependent on the temperature 

 of the surrounding medium ; it finds its limits within certain 

 extreme degrees of heat, and its greatest activity at a fixed 



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