CYCADALES 



149 



root-tip (figs. 165-67). After the coleorhiza has fractured the stony- 

 coat, the root tip digests its way through the coleorhiza and begins 

 to turn down. Entering the soil, it grows rapidly, while the stem 

 remains inconspicuous. Usually only one leaf appears. Part of the 

 cotyledon protrudes from the seed but the greater part remains in- 

 side, absorbing all of the female gametophyte and passing it on to 



/65 



Figs. 165-167. — Dioon ediile: seedling; fig. 165, the coleorhiza has fractured the 

 stony coat and the root tip has digested its way through the base of the coleorhiza; 

 fig. 166, the root end is turning down: about two-thirds of the protruding part is cotyle- 

 don and the lower part is coleorhiza, with the root visible at the base; fig. 167, later stage 

 with 3 leaves between the cotyledons; c, coleorhiza; r, root; s, cotyledons; all natural 

 size. — From Chamberlain, The Living Cycads (University of Chicago Press). 



the seedling. The cotyledons then become dry, but the stony coat of 

 the seed, with the withered cotyledons inside, remains attached to 

 the plant for a year or even longer. 



Anatomy of the seedling. — Many have studied the anatomy of the 

 cycad seedling and have described its principal features. Thies- 

 SEN,^^-* Matte, 39' and Sister Helen Angela Dorety'^^ have pre- 

 sented the most detailed accounts. Thiessen's account of Dioon 

 edule and Sister Helen Angela's of Dioon spinulosum have already 

 been mentioned in connection with the girdling of the leaf trace. 



