176 



ANGIOSPERMS. 



embryo-sac and can be distinctly recognized, no trace of the cytoplasm 

 which accompanied them in the tube can be distinguished, so that 

 the exact behavior of this cytoplasm is unknown. Consequently we 

 are concerned here solely with the union of the nuclei. 



THE FUSION OF MALE AND EGG-NUCLEI. 



We shall follow first the male nucleus which fuses with that of the 

 egg-cell. It is presumably the first male nucleus which escapes from the 

 pollen tube that unites with the nucleus of the egg, but positive proof 



on this point is want- 

 ing. In certain spe- 

 cies of Lilium, and 

 various observers 

 have shown this to be 

 true of many other 

 Angiosperms, the 

 male nucleus, when 

 observed in the egg- 

 cell, is frequently 

 sausage- shaped, 

 worm-like, or S- 

 shaped (Mottier, 

 '97), making one or 

 more spiral -like 

 turns, which is sug- 

 gestive of a worm- 

 like motion , but posi- 

 tive proof of any such 

 movement is want- 

 ing. It applies itself 

 to the nucleus of the egg, retaining the form mentioned for some time 

 (Fig. 74, A). The structure of the two sexual nuclei at this stage is 

 accurately shown for Lilium martagon in this figure. The two 

 nuclei are in the resting condition, although the chromatin of the 

 male nucleus is a little more regularly arranged. The male nuclei 

 when in the embryo-sac stain a deeper red, safranin, gentian violet 

 and orange G being used, than the other nuclei of the sac, and for 

 that reason they may be readily recognized. As fusion progresses, the 

 nuclei become quite alike in shape, size and structure (Fig. 74, B). 

 Their membranes gradually disappear at the place of contact, their 

 cavities become one, and the resulting fusion nucleus, which is in the 



FIG. 74. Fusion of sexual nuclei. 



A, vermiform male nucleus applied to egg-nucleus, Lilium martagon. 



8, egg-cell ofLHiutn candidum, showing sexual nuclei in act of fusing ; 



the nuclear membranes have disappeared at place of contact. 



