210 Cook : Potamogeton lucens 





I was unable to follow the origin and development of the 

 archesporium satisfactorily and therefore begin my discussion with 

 the functional megaspore, which is very conspicuous and located 

 some four to six layers of cells below the surface of the ovule 



{figure i). It grows rapidly and develops into the normal eight- 



nucleate sac (figures 2 y j, $) % In the four-nucleate stage (figure j) 

 the sac is considerably larger at the synergid than at the antipodal 

 end and agrees quite well in shape with Wiegand's figure 19. The 

 two nuclei of the synergid end are placed at right angles to the 

 long axis of the sac and ovule, while the two in the antipodal 

 region are placed in the same direction as the long axis. The 

 nuclei of the synergid end divide a little in advance of those of the 

 antipodal end. A number of preparations in this stage were exam- 

 ined but in no case was there a common membrane around the 

 cells in the synergid end previous to fertilization as described by 

 Wiegand. In the eight-nucleate stage the nuclei are perfectly 

 clear and well defined (figure 4). The two synergids and egg are 

 quite large, and each is surrounded by a delicate membrane. The 

 three antipodals are relatively large and have well-defined walls. 

 They were never observed in a well-defined pocket as described 

 and figured by Wiegand and by Holferty. The polar nuclei are 

 somewhat smaller than in most plants which the writer has exam- 

 ined. They unite about the middle of the sac in the usual manner 

 {figures 4, 4a). The fertilization of the egg was not observed but 

 the union of the two polar and one male nucleus was observed 

 once {figure 4b). Other preparations apparently showed the same 

 thing but upon this point the writer could not be positive. 



After a union of the two polar nuclei the newly formed endo- 

 sperm nucleus increases in size rapidly and passes into the anti- 

 podal end of the sac {figures 5, 6). In the meantime the anti- 

 podal cells disintegrate and disappear entirely {figure 6), the 

 young unicellular embryo (or pro-embryo) increases in size rapidly 

 while the synergids gradually disintegrate {figures 5, 6, 7, 8, p). 

 At this time the general appearance of the sac is strikingly similar 

 to that shown in Wiegand's figure 20. 



The primary endosperm nucleus now divides into two daughter- 

 cells which are immediately separated by the formation of a wall 

 across the sac {figure 7). The daughter-nucleus on the synergid 



