CO-OPERATION AND COMPETITION 

 COOPERATION OF NUCLEf 



8 + f/5 



Fig. 49. — Pollen grains adhering in dyads and tetrads in Uvuhria grandijlora (x = 7) 

 after a heat shock which has deranged the second division spindle and consequently 

 anaphase separation and wall-formation. The pairs of nuclei in the incompletely 

 divided cells are unequal but complementary and therefore come into mitosis at 

 the same time. In the two bottom cells an acentric fragment is present and the 

 sum of the pair of nuclei is unbalanced, with less (in the prophase on the left) or more 

 (in the metaphase on the right) than a diploid complement. One of the resting cells 

 shows double nuclei, but all have perfect wall formation and are not synchronized 

 (after Barber, 1941). 



199 



