350 THE FLOWER 



prothallus is reduced to the lowest possible terms, for 

 it consists of nothing but the single mother cell of the 

 two gametes and the nucleus of the grain which later 

 functions in forming the pollen tube. 



The nucleus of the megaspore (embryo sac) divides 

 by three successive divisions to form eight nuclei 

 (Fig. 59, C, a-e), a group of four at each end of the 

 sac. Two of these nuclei, one from each group of four, 

 fuse together in the centre to form the secondary nucleus 

 of the sac, the other three of each group remain together 

 and accumulate cytoplasm, so that two groups of three 

 cells are formed one at each end of the sac. The 

 three cells at the micropylar end of the sac form the 

 egg apparatus, the cell farthest from the micropyle 

 being the egg (female gamete), the other two the 

 synergids. 1 The three cells at the opposite end of the 

 sac are called the antipodal cells (Fig. 59, D, ant.). 



It is to be noticed that while one cell only of the 

 eight normally functions as a female gamete, its nucleus 

 is the sister of a nucleus which fuses in the centre of 

 the sac with a corresponding nucleus from the antipodal 

 group. The secondary nucleus so formed undergoes, 

 as we shall see presently, a further development. 

 As an abnormality, also, one of the synergidae or one 

 of the antipodal cells may fuse with a male gamete, 

 thus itself acting as a gamete. We must, therefore, 

 probably regard the two groups of cells as broods of 

 four gametes, only one of the eight being normally 

 functional as a sexual gamete, i.e. fusing with a male 

 gamete, though two others normally behave in a gamete- 

 like way. This recalls the brood of eight eggs in 



1 Synergidae (Greek ovv, with, and epyov, work) = " co-operators," 

 because these two cells are supposed to assist in directing the pollen 

 tube to the egg. 



