CELLULAR DIFFERENTIATION IN THE SLIME MOLD 



229 



Histograms of a stable diploid strain (RA) of D. discoideum are in- 

 cluded for purposes of comparison. The NC-4 amoebae are seen to be 

 unimodally distributed about a mean diameter of 16 microns, with a 

 scattering of a few cells far up into the diploid size range. The fre- 

 quency of individuals classifiable as I-cells remains at a steady-state 

 level of 1:2000 in both the R-cell clones and the carried NC-4 stock. 

 Ploidy was determined by the examination of metaphase figures fixed 



60 



40 



20 - 



_n 



40 



20 



60 



40 



20 



NC-4 



J R-cells 1_^ 



10 I6l5jj±2 5 



28 35 3;j±l5.4 

 I-cells 



r-v-i 



46 



^ 



26 



I-2A 



1.1 ^ i < I i i 4 i 4 ,1 ' ' ' 



12 



20.8^i± 3 2 



35 



r 



RA 



>— ■ r-i 



16 



21 4>j±2 6 



32 



Figure 3. Size distributions of myxamoebae (Sussman et at., 1960). 

 Abscissae: mean cell diameters. Ordinates: number of cells. The means of 

 mean diameters and standard deviations are given for each strain. The insert 

 at the upper right is a histogram of those cells first recognized as I-cells by 

 inspection and then sized. The dotted line at the upper left was obtained by 

 random sampling in the usual manner. 



