BACTERIA 



sap of other plants, and cannot exist by their own labours 

 at all. Moreover, we can find almost every conceivable state 

 of transition. These can be clearly and definitely traced from 

 those plants which depend on the labour of their own roots 

 and leaves to others which have no leaves, and which con- 

 sist merely of one large flower and a large adhesive sucker 

 fixed on some one else's root. 



The difficulty is very often to know where to draw the 

 line. Probably no flowering plant is quite independent of 

 the labour and work of its neighbours. As we have tried to 

 show in another chapter, a long preliminary cultivation 

 by bacteria, lichens, and mosses is required before flowering 

 plants can develop on bare rock. That is also necessary in 

 all cases where the soil is mineral or iiiorganic, without any 

 organic dust or fragments of vegetable or animal matter. 

 Bacteria must always begin the work by preparing nitrates 

 and other salts. 



So that only those bacteria which weather rocks can be 

 called really free and independent. But other bacteria, such 

 as those which cause typhoid, anthrax, hydrophobia, etc., 

 are the best possible examples of pure cannibals, or, as they 

 are usually described, parasites. 



This last word is derived from a peculiar class of people 

 in ancient classical times, who used to appear whenever a 

 meal was going to begin, and received food without giving 

 anything in return. They are represented by our tramps or 

 by the " sundowners " in Australia, who appear as soon as the 

 evening meal is ready and when there is no possibility of 

 going any further on their journey. 



The way in which plants became parasites or cannibals is 

 a very interesting part of plant life, and we shall try to 

 trace some of the various stages. 



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