1907] PACE— FERTILIZATION IN CYPRIPEDIUM 361 



egg. Fig. §4 shows a two-celled embryo and the primary endosperm 

 nucleus in late prophase. At the three- or four-celled stage of the 

 embryo, the endosperm nucleus shows a spindle forming (jig. jj), 

 which is almost complete and is very broad; the chromosomes 

 (approximately thirty-three) are probably in metaphase. On the 

 other hand, the primary endosperm nucleus may reach the anaphaso 

 before the fusion of the male and female nuclei, as one of my sections 

 shows, the male nucleus not having left the pollen tube, and both it 

 and the egg nucleus with spirems forming. 



rm spindle shows a wall (fig 



phemeral 



nucleate endosperm. The endosperm nuclei are relatively large, 



r 



as would be expected from the large amount of chromatin used in 

 their formation (figs. 57, j8), one in fig. 57 measuring 17 X 23 fi. 

 For this reason they are not likely to be confused with other nuclei of 

 the sac. The two-nucleate stage of the endosperm may be reached 

 at any stage of the embryo between two and twenty or more cells. 

 The figures for the second di\dsion of the endosperm were not seen, 

 but the four-nucleate stage was found in a few sacs {fig, j8). From 

 the appearance of these nuclei it is altogether probable that another 

 division may take place, for they are apparently beginning the forma- 

 tion of the spirem for the next di^lsion, and are large, vigorous- 

 looking nuclei. 



While the presence of endosperm nuclei is quite common, it is not 

 difficult to select a series that would indicate the possibility of their 

 failure. An embrvo of several cells with the Drimarv endosperm 



(fig 



may 



(fig 



spirems, although there is no evidence of fusion further than the 

 contact. In fig. 6i one of the nuclei, probably the male nucleus, 

 has been delayed in reaching the other two; yet some suggestion 

 of the spirem is evident in all three. Fig. 62 shows a sac which is 

 almost filled by the embryo, and at the base are three nuclei which 

 are probably the constituents of the triple fusion which has not taken 

 place; it is barely possible that they are endosperm nuclei, but there 

 is no evidence of a fourth nucleus. If these are not endosperm nuclei, 



