130 



THE LIVING CYCADS 



up on a ''cotyledonary tube." The growth of the tube 

 does not continue long, but the cotyledons grow rapidly, 

 and when the seed is mature the length of their free 

 portion is several times that of the tube. The two 

 cotyledons are closely applied to each other by their 



Fig. Gg.—Dioon edule: later stage in the development of the embryo, 

 showing the flat stem tip, the beginning of the two cotyledons, and farther 

 back a swollen region which marks the beginning of the coleorhiza. 

 Highly magnified. 



edges throughout nearly their entire length, but at the 

 tip they bend outward, in some species sHghtly, and in 

 others so decidedly that many cycads could probably 

 be distinguished by their cotyledons. 



' It is some time after the appearance of the cotyledons 

 that the stem tip gives rise to any leaves^ Several of 

 the first leaves, whose embryogeny looks promising, are 



