254 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



Some botanists have attempted to relate the occurrence of the 

 Nuclear or the Cellular endosperm to the spatial conditions (Raum- 

 verhdltnisse) in the embryo sac. According to them, long and nar- 

 row embryo sacs generally have a Cellular endosperm, while broad 

 and short embryo sacs have a Nuclear endosperm. This difference 

 is attributed to the fact that in broad embryo sacs the phragmoplast 

 is unable to form a complete partition across the embryo sac and 



Fig. 144. Development of endosperm in Lappida echinata. A ,B, first division of 

 primary endosperm nucleus; partition wall ends blindly, without reaching down to 

 base of embryo sac. C, more advanced stage, showing cell formation in upper part 

 and free nuclei in lower. (After Svensson, 1925.) 



soon disappears. While such an explanation may seem plausible 

 at first sight, it fails to take account of those cases in which the first 

 wall is longitudinal and bisects the embryo sac from pole to pole 

 (Fig. 126A), nor can it apply to others in which the Nuclear as well 

 as the Cellular types are both found in the same species and some- 

 times even in the same ovary (see Svensson, 1925; Sabet, 1931). 



V. S. Rao (1938) suggested a correlation between the type of endo- 

 sperm and the rate of growth of the embryo. According to his 

 survey, those plants in which growth and differentiation of the 



