GROWTH 179 



in part of a filament of Bacillus ramosus, 27.30 /j. * long at 

 the beginning, 70.03 f- long at the end of the period of 

 observation, two hours. Cell-diA'isions occurred at the 

 points indicated by the arrows. Between the first and the 

 second cell-divisions there was an increase of 6.79 /--- in 

 length, between the second and third of 9.10 ,", between the 

 third and fourth of 14.56 ,".. Between the first and second 

 cell-divisions there was a lapse of thirty-three minutes, be- 

 tween the second and third, twenty-six minutes, between the 

 third and fourth, thirty-one minutes, an average of thirty 

 minutes. The average growth during these three periods 

 was 10.14 iJ- between each two divisions, or a growth of 

 about one-third of a ij. per minute. This would appear to 

 be slow growth in comparison with that indicated by the 

 table on page 177 ; but the growth of many-celled organ- 

 isms represents the combined increase in length accom- 

 plished by a large number of comparatively large cells 

 working together. Ward's bacillus is a unicellular organism 

 of minute size. A moment's calculation will show that its 

 average increase in length in every thirty minutes, that 

 is, between each two cell-divisions, is 25%. This is certainly 

 a much higher rate of growth than is possessed at any time 

 by higher organisms,! and it is merely the average rate dur- 

 ing a half-hour. Doubtless its maximum growth is decided- 

 ly higher. Probably the growth-rate of bacteria is higher 

 under favorable conditions than that of any other group 

 of organisms. Their high growth-rate, the rapidity with 

 which they attain the size when cell-division is possible, the 

 promptness with which they divide, the immediate growth of 

 the daughter cells at a high rate, all contribute to the 

 effectiveness of these minute organisms. 



It was stated on page 166 that each cell, each kind of 

 cell, and hence each organism, has a maximum which its size 

 normally never exceeds. Let us seek a reason for this. 



* A // or micron equals yoVo millimetre. 



t Since going to press, a review of Buechner's paper (Zuwachsgrossen 

 und Wachsthumsgeschwindigkeiten bei Pflanzen. Dissertation, Leipzig, 

 1901) has appeared (Bot. Centralbl., Bd. 90, p. 500,1902) in which the 

 growth of the pollen-tube of Irapatiens Hankeri is reported at 220^ and 

 of branches of higher plants as 1% in a unit of time and length. 



