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INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



meiotically or mitotically. The reduced embryo sacs must be 

 fertilized before they can give rise to embryos. The unreduced 

 embryo sacs, on the other hand, can function without fertilization. 

 Fagerlind (1944) has recently made a detailed study of some 

 species belonging to the genus Elatostema. In E. acuminatum the 



Fig. 189. Development of aposporic embryo sacs in Atraphaxis frutescens (striped 

 portion in ovule represents hypostase). A, B, l.s. nucellus, showing archesporial 

 tissue. C,D, degeneration of cells belonging to primary archesporial tissue and 

 appearance of secondary archesporium. E, a two-nucleate haploid embryo sac 

 accompanied by uninucleate diploid embryo sac. F, young aposporic embryo sacs. 

 G, nucellus, showing three embryo sacs — one diploid and two-nucleate, another 

 haploid and four-nucleate, and the third haploid and eight-nucleate. {After 

 Edman,1931.) 



megaspore mother cell enters into a meiotic prophase, but because 

 of the occurrence of certain irregularities the derivative cells are 

 nonviable and soon degenerate. The adjacent cells of the nucellus 

 divide mitotically to give rise to unreduced embryo sacs (somatic 

 apospory), but these also usually degenerate, resulting in consider- 

 able sterility. In E. eurhynchum there is little or no tendency 



