13S MORPHOLOGY OF ANGIOSPERMS 



There is also indication that the two male nuclei mav be- 



*j 



come differentiated in form, as in the case of Alisma, in which 

 Schaffner 2S found the upper male nucleus in the pollen-tube 

 elongated or spindle-shaped, and the lower one spherical. It 

 is also probable that in cases of double fertilization the two 

 male nuclei often assume different forms in the embrvo-sac. 

 Four male nuclei have been reported by Strasburger 12 as some- 

 times occurring in Camassia Fraseri, and Chamberlain 32 has 

 observed three nuclei within a single male cell in Lilium dura- 

 tion (Fig. 63, C). This recalls the spermatogenesis of Gymno- 

 sperms, in which the generative cell gives rise to a stalk cell 

 and two male cells, but it may have no further significance 

 than that any active cell may be induced to divide by favorable 

 conditions. 



The morphology of the structures included in the male 

 gametophyte of Angiosperms is obscure. In 1884 Stras- 

 burger 12 suggested that only an antheridium is developed 

 within the pollen-grain, the vegetative or prothallial tissue, rep- 

 resented in many Gymnosperms, having been entirely sup- 

 pressed. The same view has been developed in several papers 

 from this laboratory, and in 1898 Belajeff 36 reiterated it in 

 a discussion including both Gymnosperms and Angiosperms. 

 According to this view, the larger tube-cell is the antheridium 

 wall that develops a tubular outgrowth, used at least in Angio- 

 sperms as the carrier of the male nuclei, while the generative 

 cell and its product is the spermatogenous part of the antherid- 

 ium. It is not exact to say that according to this view the 

 whole pollen-grain is an antheridium, but that in its germina- 

 tion the pollen-grain develops only an antheridium. 



Another view, which seems to be the only alternative, is 

 that while only an antheridium is present its sole representative 

 is the generative cell, the tube-cell not being any more a part 

 of the gametophyte than is the embryo-sac. The divergence 

 between the two views, therefore, has to do only with the nature 

 of the tube-cell. In any event, it is important to note, as contra- 

 dicting a very common statement, that the pollen-tube is not the 

 male gametophyte. 



The development of the pollen-tube and the passage of the 

 male nuclei to the embryo-sac are so directly connected with 

 fertilization that they will be considered in the next chapter. 



