POSITION— RELA T ION SHIPS 



23 



The food of bacteria is always taken up in solution by 

 diffusion through the outer covering of the cell, as it is in all 

 plants. Plant cells never surround and engulf particles of 

 solid food and digest them within the cell as many single- 

 celled animals do and as the leukocytes and similar amoeboid 

 cells in practically all multicelled animals do.^ 



One of the most generally recognized differences between 

 animals and plants is with respect to their energy relation- 

 ships. Plants are characteristically storers of energy while 

 animals are liberators of it. Some bacteria which have the 

 power of swimming in a liquid certainly liberate relatively 

 large amounts of energy, and in the changes which bacteria 

 bring about in the material which they use as food con- 

 siderable heat is evolved ("heating of manure," etc.. Chapter 

 XI). Nevertheless, the evidence is good that the bacteria 

 as a class store much more of the energy contained in the 

 substances actually taken into the body cell as food than is 

 liberated in any form. 



The above arguments for classifying bacteria may be 

 briefly summarized as follows: 



Resemblances to Plants. 



1. Like the lowest algse in being sin- 



gle celled, having similar cell 

 forms and similar cell group- 

 ings. 



2. Like the yeasts in being unicellu- 



lar and without chlorophyl and 

 having similar metabolism. 

 The fission yeasts form a con- 

 necting link. 



3. Like the molds in not having clilor- 



ophyl and having similar metab- 

 olism. The higher bacteria form 

 a connecting link. 



4. Chemical composition is similar to 



fungous plants. 



5. Rather storers of energy than lib- 



erators of it. 



6. Food is always taken into the cell 



in solution. 



Resemblances to Animals. 

 Like the protozoa in being uni- 

 cellular. 



MotiHty is more like that of 

 certain protozoa than that 

 of protophyta. 



3. Spore formation corresponds 

 rather to encystment of the 

 protozoa than to spore form- 

 ation of fungous plants. 



It should be evident that the preponderance of resemblances 

 is in favor of placing the bacteria among the plants. 



1 Myxomycetes excepted, and they may just as well be considered animals 

 — Mycetozoa. 



