MICROORGANISMS AND FERMENTATIONS 3 



separate daughter cells of equal size, which in their turn grow 

 longer and divide, the process being repeated indefinitely. This 

 mode of reproduction is known as fission. Yeast cells, on the 

 other hand, reproduce by budding, or gemmation ; small round 

 outgrowths appear and continue to develop until they attain the 

 size of the mother cell (see Fig. 2). 



In the moulds we generally find growing points as in the higher 

 plants ; only the outer cells are capable of reproduction, which 

 mostly takes place by fission and only rarely by budding. 



Spore Formation. As the higher plants form seeds, so many of 

 the microorganisms form spores, the function of which is to 

 preserve the species under adverse conditions. Spores are 

 accordingly more resistant to the influence of desiccation, poisons 

 and high temperatures than the ordinary cells. Two distinct 



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FIG. 4. Growing Top Yeast. (After Mitscherlich.) I. At 7 p.m. II. Next 

 morning, 8 a.m. III. 9 a.m. IV. 10.15 a.m. V. Noon. VI. 3.30 p.m. 

 VIT. 8 p.m. VIII. 9 p.m. IX. 10 p.m. X. 11 p.m. 



types are found : endogenous and exogenous spores. It is com- 

 paratively seldom that the cell becomes completely changed into 

 an Arthrospore, absorbing reserve food material freely and 

 thickening its wall 1 . Endogenous spores are formed inside a cell 

 while exogenous spores arise as constrictions on the end of a cell. 

 Bacteria only form spores of the first mentioned type, only one 

 spore appearing in each cell. If the spore causes the cell to bulge 

 out locally, drumstick (Plectridium) or club-shaped (Clostridium) 

 formations arise according as the spore lies at the end or in the 

 middle of the cell. Germination in a direction approximately at 

 right angles to the length of the cell is said to be lateral, and 

 germination from the end polar. The yeasts likewise form 

 endospores only, but several spores, up to ten in number, may be 



1 In this connection it may be mentioned that, according to Preisz' 

 investigations ( " Centralblatt f. Bakt.," 1 Abt., 1918, Bd. LXXXIL, p. 321), 

 the spore proper (the refractile body) is always only condensed reserve food 

 material ; outside this may be demonstrated a mass of protoplasm from 

 which growth proceeds. 



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