ii6 Minnesota Plant Life. 



bread or food-materials, is often due to the growth of bacteria 

 with the power of secreting a red dye. When such spots ap- 

 peared, very naturally, upon sacramental bread in the churches 

 and monasteries of the Middle Ages, it was regarded as an ex- 

 tremely l)ad omen, and this same phenomenon in earlier times 

 and in older civilizations was no less terrifying. Many an un- 

 fortunate man or woman has been seized and put to the torture 

 on account of these red bacteria, and even yet their presence is 

 regarded with superstitious horror in most parts of the world. 

 Besides the red forms there are those capable of producing 

 blue, pink and yellow dyes which are alike conspicuous. Such 

 growths will appear "spontaneously," developing from atmos- 

 pheric germs, upon the surface of steamed potatoes kept in moist 

 places where they occur as more or less flattened hemispherical 

 drops of colored slime. If a bit of slime is placed under a power- 

 ful lens it will be discovered to consist of unnumbered millions 

 of tiny bacterial cells, imbedded in a common jelly of their own 

 secretion. The shapes which such little masses of bacteria take 

 when growing upon a steamed potato, or a piece of bread, may 

 be compared with the tubercles formed in the lungs in cases of 

 consumption. The mass of bacteria becomes inclosed, as it were, 

 within a shell of its own excrement and may be thus prevented 

 from extending uniformly and continuously over the surface of 

 the potato. 



Purple bacteria. One very remarkable kind of color-bacte- 

 ria deserves especial notice since it is an exception under the 

 general (Icfmition of fungi given above. Such bacteria are 

 known as purple bacteria and they have the ability to develop 

 in a thin layer just inside their cell-walls, a remarkable organic 

 substance known as bacterial purple. It has been found that 

 germs provided with bacterial purjjle in their cells are al^le to 

 assimilate carbonic-acid-gas in the dark as well as in the light. 

 The number of such germs is small, but they are of extraordi- 

 nary interest because their behavior is similar to that of green 

 l)lants which deconi])osc carbonic-aoid-gas in sunliglu or under 

 the electric arc, using the products in starch-manufacture. Bac- 

 teria with bacterial purple are, therefore, independently nour- 

 ished plants in very much the same sense that green plants are. 

 and tlie\- can use in their nutrition nuieh the same simple food 



