Feb., 1903.] Agrostemma githago. 367 



top divide again so as to form a quadrant (Fig. 14). The upper 

 cell is the next to divide by a longitudinal wall (Fig. 15), and 

 this is followed by a division of the fourth cell from the top 

 (Fig. 16 j. Repeated longitudinal divisions now result in the 

 spherical embryo made up of live tiers of cells (Figs, 17, 18, 20). 

 In the meantime the suspensor has elongated by transverse 

 divisions, but the large basal cell remains unchanged (Figs. 18, 

 20, 21, 22). 



This spherical embryo now enlarges by both longitudinal and 

 trans\'erse divisions in the different tiers until the appearance of 

 the cotyledons, when it begins to elongate (Figs. 21, 22 and 25). 



The cotyledons develop in the typical dicotyl manner on oppo- 

 site sides and at the summit of the spherical embryo, and with 

 the plumule between. At the same time the calyptrogen begins 

 to develop in the row of cells next to the suspensor, gi\'ing rise 

 to a well-developed root-cap. The embryonic tissues are quite 

 distinct ; the dermatogen, periblem and plerome being easily rec- 

 ognized. At about this time the suspensor disappears, and the 

 embr^'O elongates and becomes very much curved in the embryo- 

 sac, the inner cotvledon being slightly shorter than the outer one 

 (Fig. 26). 



It will be easily seen that there is very little similarity between 

 the development of the archesporium, the ovules or the embryo 

 of Agrostemma githago and Claytonia virginica, the embryonic 

 development being entirely different. The embr^^o of A. githago 

 resembles in general appearance the embryos of Cruciferae as 

 represented by Capsella and Alyssum. 



I wish to express my thanks to Prof. J. H. Schaffner, of the 

 Ohio State University, for many valuable suggestions in this study. 



CONCIvUSIONS. 



1. The archesporium develops as one, two or three cells, of 

 which all but one are absorbed. 



2. The sac is formed from the one remaining archesporial cell 

 in the usual manner. After the formation of the eight-cell stage, 

 the enlargement of the sac is from one side and at right angles to 

 the original long axis. 



3. With the formation of the sac, the ovule enlarges from the 

 micropylar end, thus leaving the sac deeply embedded in the 

 nucellus. A short beak is formed, which projects through the 

 micropyle. Two or three rows of cells degenerate to form a 

 passage for the pollen tube. 



4. The embr)'o is at first filamentous, the basal cell being very 

 large. The four or five cells next to the apex divide longitudi- 

 nally, forming the four or five tiers of a large spherical embr3'0. 

 The cotyledons and the root-tip are formed in the usual dicotyle- 

 donous method. Soon after the appearance of the cotyledons the 

 suspensor degenerates. 



