138 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



Sometimes one or all of the antipodal nuclei move up and function 

 as supernumerary polar nuclei; or the secondary nucleus fragments 

 to form a group of micronuclei of varying sizes. Supernumerary 

 egg cells and synergids have also been noted. Very rarely, the 

 embryo sac shows a reversed polarity, with the egg apparatus 

 differentiating at the chalazal end and the antipodals at the micro- 

 pylar. As examples may be cited Atamosco texana (Pace, 1913), 

 Fuchsia marinka (Tackholm, 1915), Lindelofia longiflora (Svens- 

 son, 1925), Saccharum officinarum (Dutt and Subba Rao, 1933; 

 Narayanaswami, 1940), Woodfordia floribunda (Joshi and Venka- 

 teswarlu, 1935), Eriodendron anfractuosum (Thirumalachar and 

 Khan, 1941), Heptapleurum venulosum (Gopinath, 1943), and 

 Crinum asiaticum (Swamy, 1946). In certain other plants, a nor- 

 mal egg apparatus is differentiated at the micropylar end, but two 

 of the antipodal cells also look like synergids and the third resembles 

 an egg, (Fig. 94A) so that the embryo sac apparently shows two 

 egg apparatuses, one at each end. Poa alpina (Hakansson, 1943) 

 sometimes shows the reverse condition, i.e., the occurrence of two 

 groups of antipodal cells, one at the micropylar end and the other 

 at the chalazal. Embryo sacs of the latter type are functionless, 

 however, and do not produce embryos. 12 



The embryo sacs of the Viscoideae (Fig. 65), some members of 

 the Balanophoraceae (Figs. 60, 61), and a few saprophytic genera of 

 the Gentianaceae (Fig. 90) also appear to be inverted. Oehler 

 (1927) has given the correct explanation when he says that the 

 ovules of Leiphaimos and Cotylanthera, although seemingly ortho- 

 tropous, are in fact anatropous, and that the inversion in the polar- 

 ity of the embryo sac is only apparent but not real. 



Food Reserves in the Embryo Sac. It is usually taken for 

 granted that the angiosperm embryo sac is devoid of any appre- 

 ciable food reserves. While this is generally true, there are now 

 several records of the occurrence of starch in embryo sacs, and in 

 the families Aizoaceae, Cactaceae, Portulacaceae, Bruniaceae, Tilia- 

 ceae, Crassulaceae, and Asclepiadaceae this is a common phenome- 

 non. Dahlgren (1927, 1939) who has reviewed the subject in recent 

 years, states that the reason why starch grains have not been re- 



12 A fertilization of antipodal cells seems to have been recorded only in Nigella 

 arvensis (Derschau, 1918), but it is quite likely that it also occurs sometimes in 

 Ulmus (Shattuck, 1905; Ekdahl, 1941). 



