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INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



In plants having a multicellular archesporium, several megaspore 

 tetrads are formed and a number of megaspores may begin to en- 

 large. As examples may be mentioned the Casuarinaceae, Loran- 

 thaceae, and Rosaceae, and some members of the Rhamnaceae, 

 Rubiaceae, and Compositae. 3 Commonly most of the embryo sacs 

 become arrested in their development at a comparatively early 

 stage and only a few reach maturity. Rarely the separating walls 

 between the sacs may dissolve so that the contents become included 



A B C D E 



Fig. 58. Some stages in development of embryo sac of Epipactis pubescens. A, 

 telophase of last division in embryo sac; note that two chalazal spindles show tend- 

 ency to lie parallel to each other. B, metaphase of similar division; two chalazal 

 spindles have coalesced to form single large spindle. C,D, later stages of division. 

 E, mature embryo sac, showing egg apparatus, two polar nuclei, and single antip- 

 odal cell. (After Brown and Sharp, 1911.) 



in a common cavity. A very good example of this kind has been 

 figured in Elatine hydropiper (Frisendahl, 1927), showing an embryo 

 sac with two egg apparatuses, two pairs of polar nuclei, and two 

 groups of three antipodal cells each (Fig. 57 B). This must clearly 

 have originated by a fusion of two normally growing sacs. Similar 

 "compound" sacs have been noted by Oksijuk (1937) in Reseda alba 

 and R. inodora. Sometimes he found less than 16 nuclei, which is 



3 In Potentilla, heptaphylla (Rutishauser, 1945) as many as nine embryo sacs 

 were seen in one ovule. 



