2 34 



Mi (RPIIOLOGY 



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 



Figs. 530, 531. — Gnetum Gncmon: 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 



