Plate II. Figures 16 through 21 



Fig. 16. Transected D. mucoroides prestalk massfoUow- 

 Ing a period of reorganization exhibiting an increased de- 

 gree of staining in the prestalk and stalk cells as compared 

 to a normal D. mucoroides slug (HFAS). 



Fig. 17. An Isolated D. mucoroides cell mass composed 

 of approximately equal proportions of prestalk and pre- 

 spore cells. Following reorganization the isolate was stained 

 with HFAS. The prestalk cells did not stain cytoplasmically, 

 apparently due to the presence of the prespore cells. 



Fig. 18. Transected D. discoideum prestalk mass follow- 

 ing a period of reorganization exhibiting an increased de- 

 gree of cytoplasmic staining in the prestalk and stalk cells 

 as compared to the same areas in a normal D. discoideum 

 preculm (HFAS). 



Fig. 19. Transected D. mucoroides prespore mass, fol- 

 lowing a period of reorganization, exhibiting intense stain- 

 ing in the prespore area and cell surfaces but lacking 

 stain in the newly formed prestalk cells (HFAS). 



Fig. 20. Transected D. mucoroides prestalk mass, fol- 

 lowing a period of reorganization, exposed to D. mucoroides 

 vegetative myxamoebae absorbed HFAS. Fluorescent stain- 

 ing is completely negative. 



Fig. 21. The identical histological described section in 

 Fig. 20 but stained with HFAS. Staining exhibited by pre- 

 stalk, stalk cells and cell surfaces. 



(Fig. 18 from Gregg, Devel. Biol. 12, Zll, 1965; repro- 

 duced with permission of Academic Press.) 



cells the more we were apt to obtain prespore 

 cell differentiation. Now, if we allowed such 

 fragments as these to complete culmination and 

 form fruiting bodies, we observed small num- 

 bers of spore cells, sometimes undifferentiated 

 cells, and, of course, stalk cells. Thus, the 

 isolates produce prespore cells but the abun- 

 dance depends to a certain extent upon the 

 proximity of the transition to the prestalk- 

 prespore junction. 



The most striking thing about the reorgan- 

 ized anterior tip was the tremendous increase 

 in the amount of antigen that reappeared. Gen- 

 erally, mature stalk cells do not contain such a 

 tremendous amount of antigen as this. The pre- 



stalk cells in many of the preparations were 

 completely uniformly stained. So apparently an 

 antigen reappears during the reorganization 

 process. The fact that it appears much more 

 intensely in the stalk cells may simply result 

 from a difference in the geometry of the cells 

 relative to the prestalk cells. The antigen is 

 probably resynthesized in the prestalk cells 

 which, of course, form the stalk cells during 

 the reorganization process. 



Figure 17 shows a fragment that was iso- 

 lated, composed of about the same number of 

 prespore cells and prestalk cells. Now, we find 

 that these prestalk cells in the presence of the 

 prespore cells do not synthesize the antigen. It 



102 



