FLOWERS OF IMP A TIENS FULVA 1 7 1 



VII. The Growth of the Embryo 



After fertilization, the primary endosperm divides before the fer- 

 tilized egg. By the first division of the fertilized egg the endosperm 

 nucleus has divided to form several nuclei. The endosperm nuclei 

 are much smaller in diameter than the egg nucleus. They become ar- 

 ranged around the edge of the sac, and move upward around between 

 the egg and the micropyle (Fig. 27). The first division of the egg is 

 transverse (Fig. 27). The upper of these cells develops the suspensor, 

 and the lower the embryo. The upper cell divides transversely and the 

 lower one longitudinally. In Figure 28 three cells of a four-celled em- 

 br}-o appear. The two upper cells are derived by the division of the 

 cell which gives rise to the suspensor. The lower cell of Figure 27 has 

 divided in the plane of the paper, one of the daughter cells appearing 

 in Figure 28, and one lying immediately behind appearing in the next 

 section on the slide. The next division is longitudinal and at right 

 angles to the last, giving rise to the quadrant stage of the embryo. 

 Figure 29 is a section through the embryo at the stage when the derma- 

 togen is cut off. The section is not central, so that only one of the 

 central cells appears. The outer layer of dermatogen cells is evident. 

 The suspensor at this stage is at first two cells in length (Fig. 29). This, 

 however, rapidly increases to five cells in length (Fig. 30). In the mean- 

 time, the lower two of the suspensor cells have divided longitudinally 

 (Fig. 31). Further division gives rise to two layers of several cells. 

 Then the third cell of the suspensor divides longitudinally to form a 

 plate of at first four cells. Meanwhile the divisions of the cells of the 

 embryo have continued. The plerome and periblem are differentiated. 

 Toward the micropylar end of the embryo these layers do not arise 

 from the original embryo cell. The three lower layers of the suspensor 

 continue to divide and form the periblem and dermatogen in this region. 

 The cal>'ptrogen is later added from the outermost of these layers. The 

 two outermost cells of the suspensor remain undivided (Figs. 31 and 32). 

 These elongate, push into the micropyle, and form the suspensor proper. 

 Figure 32 shows the embryo at the time of origin of the cotyledons. 

 A peculiarity of the seeds of the genus is the existence of four side 

 roots already developed before germination. Heinricher-^ reports this 

 condition in a number of the Graminaceae and on Goebel's authority 

 in the genus Cucurhita. Heinricher found it in all species of Impatiens 

 that he investigated: — /. glanduligera, Royle, /. scabrida, D. C, /. 

 noli-tangere, L., /. parviflora, D. C., /. bicornuta, Wall, and /. balsaminay 



