144 MINNESOTA BOTANICAL STUDIES. 



though in the sac represented in Fig. 24 I suspect that there 

 were really no walls about the antipodal nuclei. However, 

 here again overlying tissues may have obscured them. Rumex 

 verticillatus gave less satisfaction in the study of the antipodal 

 region. In only one instance were three antipodals seen con- 

 stituting a three-celled mass of tissue (Fig. 21). This figure 

 represents the posterior end of a mature sac. In other instances 

 various conditions of cell-wall formation were shown in this re- 

 gion before the establishment of the sporophyte (Figs. 23, 27 

 and 28). Sometimes more than three nuclei could be distin- 

 guished within this antipodal area (Figs. 23 and 28). After 

 fertilization these cells seem to disintegrate more or less in this 

 plant, and no such typical structure was found persisting as is 

 figured for Rumex salicifolius (Fig. 33). The degenerating 

 condition of the antipodal region just after fecundation is shown 

 in Fig. 27, which is the lower end of the sac presented in Fig. 

 26. Here I was only able to make out a highly refractive area 

 with neither walls nor nuclei. As to the time when the cellular 

 membranes appear around the antipodal nuclei, I am not able 

 to state certainly because of the difficulty encountered in inves- 

 tigation, but it seems, from the facts presented and other ob- 

 served phenomena, that in Rumex salicifolius they form earlier 

 than those about the three nuclei in the anterior end of the sac. 

 In Rumex verticillatus walls were not detected till the time of 

 maturity of the embryo sac when the typical three celled condi- 

 tion (Fig. 21) presented itself, or that of three or more nuclei 

 within a common wall (Fig. 23). The antipodal area in Rumex 

 salicifolius seems to agree substantially with the third of the 

 four types proposed by Coulter* of " three comparatively per- 

 manent cells not notable for size or activity and usually associ- 

 ated with a sac decidedly narrowed at the antipodal end." The 

 antipodals of Rumex verticillatus are not so permanent, but 

 doubtless should be classed here also as should those of Poly- 

 gonum erectum. 



The size of the two polars in plants may differ as well as 

 their place of fusion. Schaffner finds the upper one larger in 

 Alisma -plantago\ and Sagittaria variabilis.\ Also he finds in 



*Coulter, John M. Contribution to the Life-History of Ranunculus. Bot. 

 Gaz. 25: 80-8 1. F. 1898. 



t Schaffner, John H. The Embryo Sac of Alisma plantago. Bot. Gaz. 21 : 

 126. Mr. 1896. 



+ Schaffner, John H. Contribution to the Life History of Sagittaria varia- 

 bilis. Bot. Gaz. 23 : 255. Ap. 1897. 



