384 



MORPHOLOGY OF GYMNOSPERMS 



all. In no case does it divide until the inner daughter cell has com- 

 pleted its division (fig. 431). This situation is so general that a row 

 of three cells occupying the position of a tetrad hardly deserves atten- 

 tion. The chromosomes have been counted in Ephedra (18, 23) 

 and in Gnetum (25), and in both the numbers are 12 and 24, conform- 



FiGS. 431, 432. — Ephedra trijurca: fig. 431, row of four megaspores, the lowest 

 beginning to enlarge; fig. 432, simultaneous free nuclear division to form the 64- 

 nucleate stage of the female gametophyte; X500. — After Land (18). 



ing to the remarkably uniform condition of gymnosperms in this 

 regard; although Jaccard (14) reports 8 and 16 for Ephedra hel- 

 vetica. If several tetrads are produced in a single ovule, several 

 megaspores may begin to function, and in the case of Gnetum several 

 contiguous embryo sacs with free nuclei may be formed, 



3. The gametophytes 



THE FEMALE GAMETOPHYTE 



The development of the female gametophyte is so strikingly differ- 

 ent in the three genera that they must be described separately. 



The course of development in Ephedra was first outlined by Stras- 

 BURGER (3), and it conforms to that described for conifers, with free 

 nuclear division, vacuolation accompanied by parietal placing, for- 



