THE EMBRYO AND SEEDLING 125 



In Dioon and Stangeria there is an evanescent seg- 

 mentation of the protoplasm of the entire embryo before 

 any permanent cell walls appear. The mechanism for 

 the formation of walls seems to be present all the time, 

 but the nuclear divisions follow in such rapid succession 

 that it does not get into operation. As the number of 

 nuclei increases, the amount of protoplasm surrounding 



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Fig. 65. — Stangeria paradoxa: free nuclear stage in the development 

 of the embryo, showing simultaneous free nuclear division below and 

 resting nuclei above. The root, stem, and leaves come from the dividing 

 nuclei; all the rest serve as nutrition. Highly magnified. 



each one becomes less and less, and the intervals between 

 successive divisions become greater, so that the ever- 

 present tendency to form walls begins to express itself. 

 The appearance of these evanescent walls is shown in 

 Fig. 66. 



In Dioon and Stangeria the walls disappear com- 

 pletely except at the base of the embryo. In Macro- 

 zamia and Encephalartos, the walls persist throughout 



