GNETALES 



127 



sac in other Gymnosperms, while the micropylar chamber still 

 contains only free nuclei (Fig. 91, 7). 



It is in this stage that fertilization occurs, for the free 

 nuclei, or presumably free cells, of the micropylar chamber are 

 all apparently potential eggs. Archegonia, therefore, are no 

 more developed than in Angiosperms. If fertilization does not 

 take place, the whole sac becomes filled with tissue. After fer- 

 tilization the tissue of the antipodal chamber renews its growth, 

 finally destroys the nucellar tissue, and encroaches upon the rest 

 of the sac, a small cavity at the micropylar end representing the 

 micropylar chamber. Lotsy also states that certain of the free 

 nuclei which are not fertilized organize definite cells, resembling 

 free endosperm cells of Angiosperms. The same writer also 

 calls attention to the fact that where the tissue of the antipodal 

 chamber projects in conical fashion into the constriction certain 

 structures resembling rudimentary archegonia appear. 



The species of Gnetum investigated by Karsten 10 ' llj 12 

 show still further reduction of the female gametophyte than that 

 exhibited by G. Gnemon. In these the whole sac behaves as 

 does the micropylar chamber in G. Gnemon, so that endosperm 

 tissue is not developed until after fertilization. It would seem, 

 therefore, that G. Gnemon represents a condition of the gameto- 

 phyte intermediate between its structure in Tumboa and the 

 species of Gnetum investigated by Karsten. 



The strong polarity of the sac, the occurrence of naked eggs, 

 the large or entire development of endosperm tissue after fer- 

 tilization, are all features suggestive of the Angiosperm condi- 

 tion. Especially striking in the comparison with the Angio- 

 sperm embryo sac is the occurrence of free cells at the micro- 

 pylar end of the sac, and of a compact tissue at the antipodal end. 



THE MALE GAMETOPHYTE 



The development of the male gametophyte in Gnetales is 

 practically unknown. In Strasburger's account 3 of Ephedra 

 campylopoda it is stated that in the germination of the micro- 

 spore three small cells are successively cut off, the first disor- 

 ganizing, the second persisting, and the third presumably repre- 

 senting the primary spermatogenous or generative cell. This is 

 an ordinary Gymnosperm outline, and the persistence of the 

 second vegetative cell recalls Giiikgo. 



