Fink : CONTRIBUTION TO THE LIFE-HISTORY OF RUMEX. 153 



have degenerated, the fecundated egg is extending its cell wall up- 

 ward to attach it to the anterior end of the sac and the definitive nu- 

 cleus is dividing. 



27. Posterior end of the sac whose anterior end is shown in 26. 

 The antipodals are degenerating. 



28. Embryo sac and surrounding tissue of the nucleus showing 

 mutual relations of the two structures. 



29. Anterior portion of embryo sac showing three of a probable 

 four endosperm nuclei, pollen tube ruptured at the end and the egg di- 

 viding to form the two-celled embryo. 



Plate XII. 



30. Anterior end of an embryo sac somewhat younger than that fig- 

 ured in 29 and showing the discharged pollen tube, the egg apparently 

 preparing to divide, and four endosperm nuclei with a spindle persist- 

 ing between each pair. 



3 1 . Anterior end of embryo sac showing a five-celled embryo and 

 three endosperm nuclei. 



32. Young embryo in anterior end of embryo sac showing four 

 newly formed nuclei and two persistent spindles. 



33. Embryo sac of Rumex salicifolius showing a somewhat more 

 advanced embryo, a larger number of endosperm nuclei and the anti- 

 podals still persisting. 



34. Anterior end of embryo sac showing five-celled embryo, one of 

 four observed dividing endosperm nuclei, and an undischarged pollen 

 tube which entered the sac after the egg was fecundated. 



35. Anterior end of embryo sac of Rumex salicifolius showing 

 three-celled embryo, whose middle cell is dividing, and the persistent 

 discharged pollen tube in the micropyle and extending into the sac. 



