CYCADALES 



145 



61). The body regions differentiate very slowly, the cellular condi- 

 tion, except in the suspensor region, being somewhat uniform even 

 after the topography of cotyledons and coleorhiza become easily rec- 

 ognizable (fig. 162). That the dermatogen has not yet become com- 

 pletely differentiated, even after the appearance of cotyledons, is 

 shown by the frequent occurrence of 

 periclines. 



The suspensor is a remarkable feature 

 of the cycad embryo. In an early cotyle- 

 don stage the suspensor is not a simple 

 structure derived from a single embryo, 

 but is made up of the suspensors of all the 

 embryos which have come from the ferti- 

 lized eggs of that group. In some of the 

 embryos, the suspensor elongates but lit- 

 tle ; in others, it elongates more ; and in the 

 embryo which is to be the only one to 

 reach full development the later stretches 

 of the suspensor belong only to the ma- 

 ture embryo. In a good preparation the 

 various embryos, each at the end of its 

 own suspensor, can be seen in spite of the 

 coiling and twistingof the compound struc- 

 ture made up of all the suspensors (fig. 

 163). In Ceratozamia, in the living condi- 

 tion, the suspensors can be pulled out to a 

 length of 7 or 8 centimeters. Whatever 

 the primary function of this suspensor 

 may be, it certainly thrusts the growing 

 embryo down into the gametophyte. 



Another remarkable feature of the cycad embryo is the coleorhiza. 

 It appears early in the development of the embryo, and in later 

 stages, after the embryo has reached the full length of the seed, it 

 becomes extremely hard. 



The mature seed is rather uniform throughout the family (fig. 

 164). There is an outer, fleshy seed coat which is white or creamy, 

 or which may be variously colored, with red or various combinations 



Fig. 158. — Cycas circinalis: 

 young embryo, indicating that 

 the entire egg may have seg- 

 mented and that the central 

 portion has broken down; X25. 

 —After TREUB.6''fi 



