THE EMBRYO-SAC OR FEMALE GAMETOPHYTE. 173 



period of duration. In many plants they disorganize immediately 

 after they are formed ; in others they may divide repeatedly, giving 

 rise to a larger or smaller mass of tissue which remains functional for 

 a comparatively long time. The development of the antipodal cells 

 into a mass of tissue, whose function is probably concerned with the 

 absorption and elaboration of food materials, may occur in the most 

 widely separated families a fact which goes to show that this phe- 

 nomenon is a special adaptation in each specific case and in no way 

 indicative of a closer phylogenetic relationship or a primitive condition. 



The typical embryo-sac, or female gametophyte, consists, therefore, 

 of seven cells, one of which, the egg-cell, is the female gamete, while 

 the other cells may be looked upon as vegetative or prothallial cells 

 (Fig. 73, C). The egg-cell may be regarded as the homologue of the 

 egg-cell in the Gymnosperms, and hence a rudimentary archegonium. 

 Whether the synergidas are to be regarded as rudimentary egg-cells, or 

 merely prothallial-cells, can not be determined at the present state of 

 our knowledge. 



As stated in a preceding paragraph, no attempt will be made even 

 to summarize the numerous variations in the development of the 

 embryo-sac that have been observed by the many investigators, since 

 the vast majority of these variations may reasonably be considered as 

 special adaptations, and as such are of small theoretical importance. 



One of the many interesting cases about which there is likely to be 

 much diversity of opinion will be briefly mentioned. This is found 

 in the development of the embryo-sac of Peperomia pellucida, as 

 described by Campbell ('99, '01) and Johnson (1900). In this species 

 sixteen nuclei are present in the mature embryo-sac. Of these one 

 becomes the nucleus of the egg, one the single synergid, and several, 

 usually eight, fuse to form the endosperm nucleus. The remaining 

 nuclei, according to Johnson, degenerate, but Campbell finds that they 

 are scattered in the sac, each developing about itself a cell-wall much 

 as do the antipodal cells of many Angiosperms. Johnson regards the 

 peculiarities of the embryo-sac in Peperomia as secondarily acquired 

 from the typical form, while Campbell looks upon them as primitive, 

 recalling such forms among the Gymnosperms as Gnetum gnemon 

 (Lotsy, 1900). 



In the development of the embryo-sac, as typified by Lilium, the 

 two cell-divisions which result in the axial row of four cells in Helle- 

 borus are wanting, and the question arises whether the hypodermal 

 cell of Lilium, for example, which develops directly into the embryo- 

 sac, is homologous with the hypodermal cell of Helleborus, or only 



