24 MYCOLOGY 



Cell Division mid Reproduction. — As with other plant cells in general 

 it may be said that growth is not conditioned on cell division. Growth 

 is the enlargement of the cell, not merely a swollen condition, and this 

 increase in size is within definite limits for each species, which can be 

 determined by statistic study. As long as division is not preceded 

 by nuclear division, the term fission is applicable. Certain students 

 of the group claim that there is a division of the nuclear substance 

 (Fig. 6), and Fuhrmaftn actually figures division of the nuclear mate- 

 rial in such forms as Bacillus nitri, 

 ''^- ^ Micrococcus butyricus, Spirillum 



i_^ / ® ^ W volutans and the potato bacillus. 



^ L ^' Possibly then division of the 



nuclear substance precedes that 

 of cell division, and if that phenom- 

 enon is found general, the term 

 fission is no longer apphcable. 



^. 



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Fig. 6. Fig. 7. 



Fig. 6. — Bacterium gammari. a, b, c. Cells with typical nucleus of nucleoplasm, 

 surrounded by a nuclear membrane and by one or two karyosomes also showing 

 karyokinesis; d, a filamentous bacterium from intestine of an annelid worm, Bryo- 

 drilus chlorii, each cell with a nucleus. {From Marshall. Microbiology, Second Edi- 

 tion, p. 89, after Vejdowsky.) 



Fig. 7. — Cells of Bacillus megatherimn. i. Polar granules as nuclei; 2, increase 

 in size of nucleus at time of sporulation; 3, same; 4, change in size of nucleus which 

 is surrounded by a membrane and becomes a spore. (Fro?n Marshall, Microbiology, 

 Second edition, p. 90, after Penan) 



Cell division may take place quite rapidly under favorable conditions. 

 Bacillus siihtilis divides in thirty minutes; Vibrio cholera, every twenty 

 minutes. The young cells attain full size in a short space of time. 

 Bacteriologists have estimated, that if bacterial multiplication was 

 unchecked and the division of each cell was accomplished inside of an 

 hour that in two days the descendants of a single cell would number 

 281,500,000,000, and that in three days the offspring of a single cell 

 would weigh 148,356 hundredweights. Lack of food, accumulation of 

 bacterial products injurious to the organisms that formed them explain 

 why their rapid multiplication is kept in check. 



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