THE EMBRYO AND THE SEED 



279 



The three primary antipodal cells (ant. Fig. 206, p. 258) have no 

 wall up to the time of fertilisation. Their subsequent behaviour is 

 variable. Sometimes they are at once disorganised ; but in most 

 other cases they remain functional. They may grow to large size, as 

 in many Ranunculaceae ; or they may undergo fragmentation of nuclei, 

 and even cell-division, so as to form a considerable tissue, as in the 

 Compositae and other Gamopetals. Their use appears to be to act as 

 intermediaries between the vascular supply and the enlarging embryo- 

 sac, before the endosperm is organised as a tissue. To that end they 

 sometimes develop as suckers penetrating the chalaza. But in any 

 case they only help towards the final end, which is the full develop- 

 ment of the germ. 



THE ENDOSPERM. 



The triple fusion, of the two polar nuclei with the second male 

 gamete, has already been noted (Figs. 214, 216). The first division of 



FIG. 221. 



Successive stages of development of the endosperm in Myosurus. (After Stras- 

 burger.) (i.-ii. and iv.-vii. x 400 ; iii. x 170.) i. shows state at fertilisation, 

 ii., embryo-sac much enlarged, and first division of the fusion-nucleus, iii. shows 

 embryo-sac still more enlarged ; it is on a lower scale of magnification, iv.-vii., 

 stages of cell-formation round the numerous nuclei, derived by division from the 

 fusion-nucleus. 



the resulting triple-fusion-nucleus usually precedes that of the zygote 

 (Fig. 221, i. ii.) : it is repeated synchronously, in rapid succession, so 

 that the numerous nuclei formed are found to be in corresponding 

 stages of division, and their number at any moment is some power of 

 two. Their chromosome-number is at first diploid, but the number is 



