THE FEMALE GAMETOPHYTE 



93 



if it takes place at all it is very late. In parthenogenetic species 

 of Alcliemilla (Murbeck 11S ), not only the two polar nuclei have 

 the power of motion, but the synergid and antipodal nuclei may 

 also move toward the center of the sac, forming groups of three, 

 four, or five " polar nuclei " surrounded by a common mass of 

 protoplasm. In the case represented in Fig. 42, Murbeck inter- 

 prets the antipodals to be lacking, although, according to his 

 own account, their nuclei are in the group 

 of what he calls " polar nuclei." 



Xotwithstanding some such irregulari- 

 , ties, however, the normal history of the 

 female gametophyte is so remarkably con- 

 stant that none of them can be regarded 

 as of special significance. 



The cells of the egg-apparatus are alike 

 in being pyriform and bounded by a mem- 

 brane which, for the lack of an accepted 

 English equivalent, is commonly desig- 

 nated the Hautschicht; the egg, however, 

 is vacuolate toward the micropyle, its nu- 

 cleus lying at its broad extremity, while in 

 the synergids the reverse is true (Fig. 43). 

 The size of these cells, as compared with 

 the other cells of the embryo-sac, is ex- 

 ceedingly variable, sometimes being much 

 the largest and sometimes even the small- 

 est. The morphological nature of this 

 group of cells has been much discussed in 

 the attempt to relate it to the archegonium 

 -of the lower plants. There seems to be no 

 serious objection to regarding all three 

 cells as potential eggs, only one of which 

 usually functions as such. Whether they 

 represent three archegonia, or the egg and canal cells of one 

 archegonium, seems to be pressing morphology to an absurdity. 

 The lack of any compact tissue precludes the formation of an 

 archegonium, and hence free cells organize as eggs. There 

 seems to be no need to relate them to archegonia, but merely 

 regard them as eggs produced by a gametophyte that can not 

 form archegonia. If a rigid morphology is to be applied, it 



FIG. 4.2Alchemilla sert- 

 cata. " Embryo-sac with 

 complete egg-apparatus 

 and five polar nuclei ; in 

 agreement with this, no 

 antipodals are present" 

 After MUBBECK.I" 



