124 



THE LIVING CYCADS 



sixth division, resulting in the formation of 64 nuclei, 

 various differences which seem to be characteristic of 

 the species begin to appear. 



In Stangeria, even with the 

 fifth division, resulting in the 

 formation of 32 nuclei, digressions 

 frequently occur. There is often 

 a distinct polarity, half of the 

 nuclei being in the upper third of 

 the embryo and half in the lower 

 third, while the protoplasm of the 

 middle third has no nuclei at all. 

 The two groups may behave 

 alike, dividing simultaneously, or 

 they may behave independently, 

 one group dividing while the 

 other remains in the resting con- 

 dition, the latter case causing a 

 wide variation from the regular 

 series of numbers (Fig. 64). 



In Stangeria and Cycas, after 

 the period of general simul- 

 taneous division has come to a 

 close, a hundred or more nuclei 

 at the extreme base of the embryo 

 divide once or twice more, the 

 dividing region being marked off 

 sharply from the region above, 

 in which all the nuclei are in the resting condition. The 

 entire plant, root, stem, and leaves, is organized from 

 the restricted lower region which has divided again 

 (Fig. 6s). 



Fig. 64. — Stangeria 

 paradoxa: free nuclear 

 stage in the development 

 of the embryo, showing 

 simultaneous nuclear 

 division in the upper part 

 and resting nuclei in the 

 lower. Highly magnified. 



