SI 4 



BOTANY 



cell divisions in the single, functional macrospore- mother -cell resulting from 

 the tetrad division (Fig. 498). The "n:iM.\r.Y NUCLKUS of the embryo-sac" 

 divides and the daughter-nuclei separate from one another. They divide twice 

 in succession so that eight nuclei are present. After this cell -formation commences 

 around these nuclei. Both at the upper or micropylar end of the embryo-sue 

 and at the lower end three naked cells are thus formed. The two remaining 

 "ror.Ai: NUCLEI" move towards one another in the middle of the embryo-sac, 

 and fuse to form the "SECONDARY NIVLKUS of the embryo-sac." The three cells 

 at the lower end are called the ANTIPODAL CKLLS : they correspond to tin 



Fio. 498. Development of tin- embryo-sac in l'nlii<j<iii<tin liirnfinitnui. M. Mother-cell of the 

 embryo-sac: <>ni>, embryo-sap; \ft, sterile sister-cells; c, cg^-rell ; .. syncrnid:c : j>, jwlar- 



nnclei ; a, antipodal cells; k, secondary nucleus nt tl inbryo-sac ; i-hn. clialaxa : ////'. micro- 



pyle ; ni, ii. outer and inner integuments ; /I/H. funicultis. (1-7 x 320, 8 x I'.i'i.) 



tive prothallial cells, which in Gymnosperms fill the 'cavity of the embryo-sac, 

 and in Gnetum Gneinon form a mass of tissue filling the lower end of the 

 latter. The three cells at the micropylar end constitute the EGG- APPARATUS. 

 Two of them are similar and are termed the SYNERGID^E, while the third, which 

 projects farther into the cavity, is the EOG-CELI, or OVVM itself. The synergidse 

 assist in the passage of the contents of the pollen-tube into the embryo-sac. Here 

 also the process of reduction has gone as far as possible ; in place of the more or 

 less numerous archegonia of the gymnospermous macrospore only a single egg-cell 

 is present. The significance of the synergidse is difficult to determine unless tliey 

 are regarded as archegonia which have become sterile. 



The microspores, which cannot reach the macros]>ore directly, germinate on tin- 

 stigma. The pollen-tube penetrates for the length of the style and as a rule the 



