122 



THE LIVING CYCADS 



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}) 



walls, so that the embryo, without any perceptible 



increase in size, contains 

 successively i, 2, 4, 8, 16, 

 32, 64, 128, 256, and in 

 some cycads 512 and 1,024 

 nuclei before walls begin 

 to appear (Fig. 63). 



These nuclear divi- 

 sions follow each other in 

 such rapid succession that 

 there is Httle growth be- 

 tween divisions, and con- 

 sequently the nuclei 

 become smaller and 

 smaller as they become 

 more numerous.. After the 

 number of nuclei reaches 

 128 the mathematical regu- 

 larity begins to diminish, 

 because a nucleus here 

 and there, especially in the 

 upper part of the embryo, 

 fails to divide, and 

 such nuclei become more 

 numerous as development 

 proceeds. However, the 

 proportion of such nuclei 

 is not large, and there is 

 no uncertainty in deter- 

 mining whether one is 

 dealing with approxi- 

 mately 256, 512, or 1,024 nuclei. 



liiiS 



Fig. 62. — Stangeria par ado xa: 

 first division of the nucleus of the 

 fertilized egg; the spiral, ciliated 

 band is still visible at the top of 

 the egg. Three sperms which 

 passed through the neck but did 

 not get into the egg are shown at 

 the top. Highly magnified. 



