i9«] SHARP— ORCHID EMBRYO SAC 373 



Epidendrum variegatum Hook. 



/ 



The course of development in this species corresponds in many 

 respects very closely to that recently reported for Epipactis pubes- 

 cens (Brown and Sharp 2), in which an 8-nucleate sac of the ordi- 

 nary type is derived from one or less frequently from four 

 megaspores. In Epidendrum variegatum, while the majority of sacs 



four 



from one megaspore 



Epipacti 



The archesporial cell, as in all of the other species examined, is 

 hypodermal in position, and since it cuts off no parietals it is at the 

 same time the megaspore mother cell. After passing through 

 synapsis (fig. 1) and the other prophases preceding reduction, the 

 nucleus of this cell divides-. The position of the spindle and the wall 

 formed upon its fibers is variable, which seems to be an important 

 factor in determining the nature of the subsequent development. 

 The spindle may be formed near the micropylar end of the 

 mother cell, the resulting daughter cells in this case being very 

 unequal in size, or the spindle may arise near the middle, the 

 daughter cells then being approximately equal. Between these 

 two positions of the spindle all gradations are found. 



In the event of an unequal division the subsequent development 



is as follows. The small micro 



form 



megaspores. Of these the inner one only remains functional, the 



mzmg 



divides 



(fig- 3)- The nuc 



the formation of a wall (fig. 4) and the resulting nuclei again divide 



5). At the next division 



form 



(fig. 6) cell plates appear on the fibers of all four spindles, but those 

 formed in connection with the chalazal nuclei usually disappear, 



that the antipodals are in most case 

 When the division of the megaspore 



forms 



the two daughter nuclei are left free in the same cell cavity. Vacuo- 

 lation occurs in the cytoplasm, usually in the region between the 

 nuclei (fig. 8), but at times near the ends of the cell with the two 

 nuclei at the center (fig. 9). At the division of these nuclei distinct 



