26 MORPHOLOGIC VARIATION 



these curves the logarithm of the number of yeast cells is plotted 

 against time. It may be clearly seen that with smaller seedings, 

 while the lag phase is prolonged in proportion to the decrease in 

 the size of the seeding, in all cases (except with the smallest seed- 

 ing), when once growth has been initiated, the actual rate of growth 

 is higher, as indicated by the slope of the curve. 



It is interesting to note that the size of the "seeding" has a simi- 

 lar effect upon the growth of individuals and populations of higher 

 organisms. Figure 4 shows a curve for the mean rate of increase 

 of a population of fruit flies from the data of Pearl. It is essen- 

 tially the same as the curve plotted from Brown's data for yeasts 

 (Figure 2). Figure 5 presents curves for the rate of growth of re- 

 generating tadpoles' tails with different sized stumps, taken from the 

 data of Ellis. The logarithms of total tail length have been plotted 

 against time, and the graph is comparable with the curves for yeast 

 growth in Figure 3. It will be noted that the same relationships 

 hold. With a large stump (seeding), only a small part of the tail 

 having been removed, there is no lag, and the rate of regeneration 

 is slow, as indicated by the slope of the line; with decreasing size 

 of the stump, the rate of regeneration becomes higher, and with the 

 smallest there is a distinct lag before regeneration commences. 



The age of the culture from which the inoculated cells are de- 

 rived also has an influence upon the rate of growth in the new 

 medium. Miiller first demonstrated that the duration of the lag 

 period was greater with older cultures. While Rahn and Coplans 

 found that this was true, they still observed some lag when the 

 culture used for seeding was young, and concluded that the lag 

 phase could not be entirely eliminated by using actively growing 

 cells. But Barber, isolating single cells, found that if these were 

 growing at their maximum rate when transplanted, they would con- 

 tinue to grow at that rate in the new medium, and Tenfold observed 

 that the same thing was true with ordinary culture transplants, point- 

 ing out that probably Coplans and Rahn were dealing with cultures 

 which had passed the maximum growth phase even though they 

 were young as measured in hours. Chesney has demonstrated this 

 effect of age of the parent culture most clearly in his work on the 

 lag phase of the pneumococcus. Figure 6 is a graph copied from 



