THE VEGETATIVE STRUCTURES 75 



of seeds in the nest formed by the crown of leaves. As 

 the cone decays the seeds are covered by the decaying 

 portions and germinate. The roots grow into the soft 

 tissue of the main bud and become estabhshed. When 

 several small crowns are found at the top of a vigorous 

 trunk they are almost sure to have developed in this 

 way. This behavior was not seen in any plants bearing 

 male cones. 



Fig. 23. — Dioon splnulosiim: transverse section of trunk, showing 

 large pith and cortex. The zone of wood is the broadest ever described 

 for any cycad. 



The internal structure of the trunk is as character- 

 istic as the external. A transverse section shows a 

 large pith, a comparatively narrow zone of wood, a 

 broad cortex, and a zone of persistent leaf bases con- 

 stituting the armor (Fig. 23). 



The pith and cortex contain a large amount of starch, 

 and the whole trunk has a large proportion of water, so 

 that a piece immediately sinks when thrown into water; 



