Spirogyra Cells 199 



were made by Ostwald ('08). The intervals became 

 longer as the observations continued, indicating per- 

 haps that conditions were not entirely favorable to 

 growth. These intervals were not related to the 

 rhythms of cell division. Apparently the observations 

 have not been corroborated. 



When Spirogyra filaments are measured at intervals 

 of a day or more, growth is found to be roughly pro- 

 portional to length already present. In other words, 

 growth is logarithmic; this is shown by the data of 

 Gerassimow ('01, '02) and VanWisselingh ('08, '14, 

 '20). All the descendants of an initially single cell are 

 considered together, as though no cell-divisions had 

 occurred, as in the data illustrated by figure 64. It 

 was believed by VanWisselingh ('20) that a tempor- 

 ary retardation of growth could be detected whenever 

 cell divisions occurred, similar to the retardation ob- 

 served in filaments of Bacillus ramosus (above in fig- 

 ure 16). But the retardation is very small, and growth 

 rates may be considered to be little interrupted by 

 multiplication of cells. 



Growth appears to be a prerequisite for reproduction 

 in each cell of Spirogyra. Conditions of cultivation of 

 Spirogyra have never been worked out to the point 

 where they can be thought of as ideal; but under the 

 best conditions of laboratory life, the sizes of adult 

 Spirogyra cells vary only slightly more than the sizes 

 of various ciliates and flagellates, and less than the 

 sizes of some heliozoa and bacteria. The variabilities 

 of Spirogyra dimensions are illustrated in figure 65. 



Polyploid cells. Gerassimow ('01) found that by 

 subjecting Spirogyra filaments to cold, irregular cell 

 divisions were often produced, so that some daughter 

 cells received all the nuclear material and their sisters 

 no nuclear material. He found that the former became 

 and remained much larger than the normal cells; the 



