HISTORICAL SKETCH 



13 



the former arise the egg apparatus (consisting of an egg cell and two 

 synergids) and the upper polar nucleus; from the latter, the three 

 antipodal cells and the lower polar nucleus. The polar nuclei were 

 observed to fuse in the center to form a secondary nucleus, which 



Fig. 11. Stages in development of embryo of Capsella bursa-pastoris (v = sus- 

 pensor; h-h' = hypophysis ; c-c = cotyledons ; s = stem tip ;w = radicle; the shaded 

 portions represent the dermatogen and plerome). (After Hanstein, 1870; repro- 

 duced from Sachs, 1874-) 



gave rise to the endosperm (Fig. \0H). The synergids were re- 

 garded as modified structures assisting in the process of fertilization. 

 Treub and Mellink (1880) confirmed these observations but also 

 noted certain exceptions. In a few plants they found that the 

 megaspore mother cell divides into only two daughter cells, of which 

 either the upper (as in Agra-phis patula) or the lower (as in Narcissus 



