﻿THE EMBRYOGENY OF ZAMIA. 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY. 



XLV. 

 £k John M. Coulter and Charles J. Cham be 



(with plates vi-viii) 



RLAIN. -P^ 



Our knowledge of the development of the embryo of Cyca- 

 dales is very meager, being largely included in Treub's (5) 

 account of Cycas circinalis and Ikeno's (8) of Cycas revohtta. 

 These two accounts agree in every important particular, and 

 deal chiefly with the development of the proembryo. The fol- 

 lowing facts were established : the ^^^ nucleus divides, and suc- 

 cessive simultaneous divisions give rise to a large number of 

 free nuclei ; the cytoplasm of the central region of the egg 

 becomes vacuolate and then completely disorganizes ; the 

 remaining cytoplasm becomes parietal, massing somewhat 

 toward the bottom of the t.^'g^ in this parietal layer the numer- 

 ous free nuclei are imbedded, being equidistant from one 

 another and forming usually a single layer except at the base of 

 the ^%g, where simultaneous nuclear division begins agam ; 

 later, walls appear, and the proembryo becomes a sac somewhat 

 thickened at base, but with the wall composed of one or at most 

 two layers of cells. This history differed so much from that of 

 Ginkgoales and of Coniferales as known at that time that it 

 seemed to stand somewhat stiffly apart among gymnosperms. 



A series of collections of Zamia floridana was obtained from 

 southern Florida during the spring and summer of 1902. Some 

 collections consisted only of the ovulate strobili, but in most 

 cases the entire plant was secured. As stated by Webber (ii)» 

 the ovulate strobili continue in their development for some time 

 after removal from the plant, and we have observed mitotic 

 figures in ovules after the strobilus had been lying in the lab- 

 oratory for nearly two weeks. Entire plants sent from Florida 

 in June and July were potted, and they continued to develop 



184 [MARCH 



