138 MINNESOTA BOTANICAL STUDIES. 



study of nuclear mechanism and phenomena because of the 

 small size of the cells and contained nuclei, and I have conse- 

 quently confined myself to other phases of the subject. Nor 

 have I found anything in the study that would give additional 

 evidence as to the nature of various structures within the em- 

 bryo sac so that my work resolves itself into a description of 

 the gametophyte and some comparative studies. 



Under the subject stated I shall, for the sake of relationships, 

 begin with the archesporium, which is the last term in the 

 sporophytic generation and also include stages immediately fol- 

 lowing the establishment of the sporophyte. 



So far as I know this is the first work done on the female 

 gametophyte of Rumex, or of any plant within the Polygon a- 

 cege, except Polygonum divaricatiim^ which has been investi- 

 gated by Strasburger. 



I am under obligations to Professor Conway MacMillan for 

 helpful suggestions as to technique and interpretation of struc- 

 ture and for access to the literature of the subject. 



Origin of the Macrosfore. — At about the usual stage in the 

 development of the macrosporangium, an axial hypodermal 

 cell at the summit of the nucellus begins to enlarge and soon 

 contains a larger nucleus and denser cytoplasm than the sur- 

 rounding cells ( Fig. I ). This cell constitutes the archespor- 

 ium, and in all instances examined, only one cell showed this 

 archesporial nature. The archesporium in plants may develop 

 directly into the macrospore ; it may itself become a sporogen- 

 ous cell ( mother cell ) and divide into a number of potential 

 macrospores ; or more commonly it divides first into a tapetum 

 and a sporogenous cell, each of which may divide, forming 

 a cellular tissue. In Ritmex the last order of development is 

 followed. After increasing considerably in size (comp. Figs, i 

 and 2), the archesporium divides by a periclinal wall into the 

 inner sporogenous cell (the mother cell of the macrospore), and 

 the outer hypodermal tapetum (Fig. 2). This apparently pro- 

 tective tapetum proceeds next to divide, sometimes by a peri- 

 clinal wall (Fig. 4), but no doubt much more commonly by 

 an anticlinal (Fig. 3). In no instance did I observe more than 

 four tapetal cells derived from the primary tapetum and often 

 only three, one of the two derived from tlie primary tapetum 

 apparently failing to divide. Indeed, sometimes only one tape- 

 tal cell could be distinguished at a period of development which 



