TETRAPLOIDS 129 



double germ-cell might not be able to increase to double 

 size in the germ-track of its diploid mother. The egg 

 might not then be any larger than the normal egg, but 

 have twice as many chromosomes. The embryo develop- 

 ing from this egg might not be able to get enough nour- 

 ishment to increase the size of its cells until the post- 

 embryonic or larval stages were reached, when food is 

 obtainable from the outside. Whether at this late period 

 the presence of a double set of chromosomes in each cell 

 would bring about an enlargement of the cytoplasm of 

 each cell is uncertain. In the next generation, however, 

 the eggs would develop from the beginning with a four- 

 fold set of chromosomes in a tetraploid body, and under 

 these circumstances it is conceivable that the egg might 

 grow to double size before dividing. 



It is even less to be expected, perhaps, that an imme- 

 diate increase in amount of the cytoplasm could take 

 place if the doubling of the chromosomes occurred in a 

 mature egg after it is fertilized. The embryos of animals 

 pass through a rather definite number of cell-divisions 

 before organ formation begins. If an embryo should start 

 as an egg of normal size but with double the number of 

 chromosomes, and if, in consequence of the double num- 

 ber present, cleavages should cease sooner than in the 

 normal egg when organ formation sets in, such a tetra- 

 ploid embryo would then have cells twice the size of the 

 normal embryo but only half as many cells. 



In the flowering plants where ample space and food 

 supply is present in the embryo sac, the development of 

 an egg with a larger amount of cytoplasm may have a 

 more favorable chance to take place. 



