DEVELOPMENT AND DIH E RLNTI ATION 



then both arc entirely successful. More than that, the two arc per- 

 fectly synchronized in mitosis. Thus each nucleus must be providing 

 something necessary or useful to the other, and providing it by way 

 of the cytoplasm (Fig. 49). 



none Plumhago 



yremivm 



n- hre-fushtK 4. -/ e xc ess 

 '(Sync/jo/azi/ ^"|hy|bcrc/io/- 



hyfyochaJazy 



Fig. 50. — Variations in the development of the embryo sac in Angiosperms dis- 

 regarding the number of spores which take part in it. Egg cell nucleus solid, other 

 nuclei with one dot for each haploid set. 8 means 3 mitoses before egg cell 

 formation, 16 means 4. -f and — refer to excess or deficiency in the number 

 of mitoses at the chalazal end of the embryo sac and thus imply a gradient. E, the 

 endosperm which varies in ploidy according to the number of nuclei fusing in the 

 centre. Zca, Cooper, 1938. Ocnonc, Went-Maheshwari, 1936. Plumbago, Haupt, 

 193 1, rritillnria, Westfall, 1940. Pyrcthrum, Martinoli, 1939 (</. Darlington and 

 La Cour, 1941). 



In this question of life or death the part played by the cytoplasm 

 can be as crucial as that of the nucleus. In certain hybrid species of 

 Oenothera, whose organization we shall consider later, two genetically 

 different types of germ cells are produced, say A and B, such that 



^00 



