IN THE DIVIDING ROOT-TIP CELLS OF THE ONION. 33 



(6). WARD'S WORK. 



A very important step in the analysis of vital phenomena was made 

 in 1895, when W. M. Ward/ in his classical experiments " On the biology 

 of Bacillus ramosus (Fraenkel), a schizomycete of the River Thames," 

 determined that growth {i. e., permanent increase in bulk) while in the 

 long run dependent upon cell-division, does not synchronize but rather 

 alternates with it. He measured quantitatively what other investiga- 

 tors had only caught glimpses of. 



(c). ADDITIONAL EVIDENCE. 



In 1904 W. E. Kellicott^ pubHshed, in a bulletin of the Torrey Club, 

 his paper "The daily periodicity of cell-division and of elongation in 

 the root of Allium J' In the experimentation upon which this paper was 

 based Kellicott grew onions in wet sawdust until the roots were from 

 50 to 100 mm. in length. Then, at 2-hour intervals throughout the 24 

 hours, with the temperature ranging from 14° C. at 1 a. m. to 27° C. at 

 3 p. m., he took samples of the root-tips and at the same intervals made 

 measurements of the rate of elongation of similar tips. His purpose was 

 to trace the rhythm in cell-division and the rhythm in growth, with a 

 view to determining whether (as Ward nine years previously had found 

 in Bacillus ramosus) the maximum of mitotic activity alternates with 

 the maximum of root-tip elongation. His work seems to have con- 

 firmed for the root-tip of Allium the conclusion of Ward in reference 

 to Bacillus ramosus, and thus tended to suggest the generality of the 

 principle. 



Besides counting the resting stages in selected areas, he counted also 

 the mitotically active stages, classifying them as early, middle, and 

 late. He reports no further use of this classification other than to add 

 their counts together for determining periods of comparative mitotic 

 activity. His data would hardly suffice for a study of stage duration, 

 for the observation periods were too far apart and the total number of 

 cells counted approximated only 3,000. 



Kellicott summarizes his investigations as follows: 



" 1. In the root of Allium there are two maxima and two minima in rate of 

 cell-division during the 24 hours. 



"2. The primary maximum occurs shortly before midnight (11 p. m.) and 

 the primary minimum about 7 a. m. The secondary maximum occurs about 

 1 p. m. and the secondary minimum about 3 p. m. 



"3. There is no correspondence between the rate of cell-division and slight 

 variations in temperature. 



******* 



"6. Under nonnal conditions of growth the rate of elongation of the root of 

 Allium exhibits a daily rhythm, showing two maxima and two minima durmg 

 24 hours. 



1 See ref. No. 1, p. 12. ^See ref. No. 2, p. 12. 



