74 



DIATOMS. 



in contact throw out about t^pm a cloud of gelatinous 

 material which keeps them together and excludes 

 foreign matter. The valves then separate and the semi- 

 fluid contents, protoplasm, endochrome and oil globules 

 mingle and form a spore, in some species more than one. 

 From this spore is formed one or more new diatoms much 

 larger and more robust than the parent forms. 



It seems to be the universal law of all lowly organisms 

 that the spores are much more resistant than the com- 

 plete forms to adverse influences — heat, cold, dryness, &c. 



The spores of bacteria are much harder to' kill tbaa thQ 



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