I40 



GYMNOSPERMS 



Free nuelear stage. — Following fertilization there is a period of free 

 nuclear division. The divisions are simultaneous, so that the number 

 of nuclei is, theoretically, 2,4,8, 16,32, 64, 128, 256, 512, and, in some 

 cases, 1 ,024. The earlier divisions are very regular and the numbers 

 of nuclei are about what should be anticipated; but, in Dioon ednlc, 

 the eighth, ninth, and tenth divisions are irregular, some of the 



Figs. 150 and 151. — Slangeria paradoxa: free nuclear stage of embryo; fig. 150, 8- 

 nucleate stage, showing simultaneous mitoses in two groups of nuclei; very definite 

 polarity with simultaneous mitoses in both groups of nuclei; fig. 151, polarity with 

 mitoses in upper group but not in the lower; X42. — .\fter Chambkrlain."» 



nuclei failing to divide, especially in the upper part of the embryo. 

 'J'he number beyond the 256 nucleate stage is likely to be less than 

 the theoretical estimate, because some of the nuclei fail to divide. 



In Stangcria there is often a distinct polarity, the nuclei being in 

 two groups (figs. 150, 151). If the nuclei in the lower group divide, 

 those at the top do also; but those at the top may divide without a 

 corresponding division in the lower group. A glance at the illustra- 



