234 



MORPHOLOGY 



The three genera differ widely in this regard, and therefore must be 

 considered separately. 



Ephedra. The female gametophyte is developed as in other gymno- 

 sperms, with free nuclear division (up to 256 nuclei), parietal wall 

 formation, centripetal growth, and differentiation of the endosperm into 

 distinct " micropylar and antipodal 

 regions. In this case, however, the 

 antipodal tissue (nutritive) is rela- 

 tively small-celled and compact, and 

 the micropylar tissue is more loosely 

 organized and has thinner walls. In 

 this loose micropylar tissue usually 

 two archegonia are formed, their 

 very long, many-tiered necks extend- 

 ing to the pollen chamber described 



530 531 



FIGS. 530, 531. Gnetum Gnemon: 530, diagrammatic section of ovule, showing the 

 two integuments (inner one forming the micropylar tube), nucellus with disorganized tip, 

 and deep-placed embryo sac, beneath which is a mass of feeding (glandular) tissue; 

 531, enlarged view of same embryo sac (ready for fertilization), in which the female 

 gametophyte consists of free nuclei (each a potential egg), and below which is the mass 

 of feeding tissue. After COULTER. 



above (figs. 528, 529). In the organization of the egg, a ventral nucleus 

 is cut off, and not a ventral cell. 



Tumboa. The female gametophyte is developed as in Ephedra as 

 far as wall formation ; but in the differentiation of the endosperm into 

 two regions (one fourth micropylar and three fourths antipodal) there 

 is very incomplete wall formation. As a consequence, the cells of the 



