158 MORPHOLOGY OF ANGIOSPERMS 



stant, and Strasburger, 43 in examining the process in living- 

 material of Monotropa, demonstrated the passage of the male 

 nucleus in the streaming protoplasm of one of the cytoplasmic 

 strands connecting the primary endosperm nucleus or the polar 

 nuclei with the egg-apparatus. This is confirmed by Guig- 

 nard, 53 who has described and figured the very small male 

 nucleus passing down the broad cytoplasmic strand that con- 

 nects the egg-apparatus with the antipodals and envelops the 

 primary endosperm nucleus in Nigella, Damascena, Ranunculus- 

 Cymbalaria, and Anemone nemorosa, and which is doubtless 

 true of the other Ranunculaceae. It seems probable that the 

 male nucleus is generally carried along one of these strands ; but 

 it is not improbable that the vermiform nuclei occasionally 

 acquire some power of independent motion. It is during this 

 passage that the male nucleus may increase much in size 

 (Thomas, 44 Ikeda 58 ) and may even assume the vermiform 

 character; although all such changes may have occurred before 

 discharge from the pollen-tube, even in the pollen-grain, as 

 observed by Merrell 35 in Silphium. The male nucleus, how- 

 ever, may retain its small size and oval form even in contact 

 with the polar nuclei, as observed by Guignard 32 in Endymion, 

 and by other observers since. In Juglans Karsten 55 believes 

 that in all cases the polars are fertilized before the egg ; but in 

 Nicotiana Tabacum Guignard 56 reports that sometimes the egg 

 is fertilized first and sometimes the polars, so that probably 

 there is no definite order in the two fusions. 



Every possible order in the fusion of the three nuclei has 

 been observed, so that the triple fusion is brought about in a 

 variety of ways. As might be expected, it is often the case that 

 the polar nuclei have already fused when the pollen-tube enters 

 the embryo-sac, and the male nucleus unites with the fusion 

 nucleus, as in Tricyrtis, Ranunculaceae, Datura, Erigeron, Sil- 

 phium, etc. ; although even in this case the polar nuclei may not 

 always lose their individuality. The two polar nuclei and the 

 male nucleus have also been observed to fuse all together, as in 

 Zea (Guignard 48 ) and other plants, in which the vermiform 

 male nucleus seems to bind the polar nuclei together. In Nicoti- 

 ana (Guignard 56 ) the male nucleus comes in contact with either 

 polar nucleus or both. In Lilium Martagon the male nucleus 

 usually fuses first with the upper polar nucleus, and later the 



