56 Univcrsil !/ of ('(ilifdniid I'lihlicdfidiis in liohnn/ fVoi,. 7 



epidermis and eventually aid in deliiseeiiee. As tlie tapelum degen- 

 erates anther sap appears and sometimes is very abundant when the 

 pollen grains are about half grown, hut disappears soon after the 

 division of the microspore nucleus. From tlic early part of December 

 to anthesis, late in February, no changes take ])lace in the appearance 

 of normal i)ollen. During this period, however, the cells of the endo- 

 thecium are increasing theii- radial diametei- and develop radial thick- 

 enings on their walls (pi. I), fig. 2). The method of dehiscence of the 

 auther has been described above. 



At the time when the pollen mother-cells are dividing the o\^iles 

 already have the nucellus and the integuments well differentiated 

 (cf. Coulter and Chamberlain, 1903, p. 52). The megaspore mother- 

 cell is discernible in the third layer of cells immediately under the 

 apex of the nucellus. It may be recognized by its slightly increased 

 size, nearly square shape, and large nucleus with rather open retic- 

 ulum (pi. 7, fig. 9). Nucellus and integuments grow with gradually 

 increasing rapidity until the arrival of the flowering season, but the 

 megaspore mother-cell changes but little in size and appearance at the 

 time the shoot appears above ground (cf. Alden. 1912. p. 448). As 

 the stem and leaves begin their rapid growth above ground the mega- 

 spore mother-cell begins to grow rapidly and take on an elliptical 

 form. When the leaves are becoming fairly well unfolded the hetero- 

 typic division occurs (pi. 7, fig. 10). Sufficient material was not ob- 

 tained for a critical study of this stage and the succeeding stages in 

 the formation of the embryo-sac, but from the fact that the heterotypic 

 division takes place after the shoot has appeared above ground and 

 that a large embryo-sac is present when the flower unfolds it seems 

 safe to assume that the female gametophyte in T. sessile var. giganieum 

 follows practically the same course of development as Ernst describes 

 for the female gametophyte in T. grandiflorum. 



Actual confirmation of Ernst's conclusions can be made only with 

 regard to the earlier stages in the maturation of the female gameto- 

 phyte. Thus I have seen the formation of the cross-wall following the 

 first or reduction division of the megaspore mother-cell (cf. pi. 1, 

 fig. 10). This wall is curved and arches upward as the inner cell 

 develops at the expense of the outer (cf. Ernst, 1902, p. 14, ])1. 5, figs. 

 143 and 144). The inner, persistent cell enlarges, takes on an oval 

 form and becomes the young embryo-sac (cf. Heatley, 1916). During 

 its increase in size free nuclear division takes place to produce first a 

 binucleate embryo-sac. Ernst reports that the young embryo-sac con- 



