THE MALE GAMETOPHYTE 169 



around them. Tschernojarow (1915), Dahlgren (1916) and Ishi- 

 kawa (1918) demonstrated the occurrence of male cells in Myosurus, 

 Plumbagella, and Oenothera respectively. Wulff (1933) and Finn 

 (1935, 1940, 1941), who are the most active workers in this field, 

 categorically state that the occurrence of male cells may be assumed 

 in all angiosperms, and assert that in those plants in which only 

 male nuclei have been reported, proper methods of fixing and staining 

 will eventually reveal the thin cytoplasmic sheath around them. 



Vegetative Nucleus. Earlier authors took it for granted that the 

 vegetative nucleus (often called "tube" nucleus) had an important 

 role in directing the growth of the pollen tube. Present evidence 

 seems to indicate, however, that its functional importance had been 

 greatly exaggerated. 



The vegetative nucleus is not always in the distal end of the 

 pollen tube (where it would be most expected if it had any important 

 function in directing the growth of the tube) but frequently lies 

 considerably behind the male gametes. When the tube becomes 

 branched as in Aconitum, Cucurbita, and Papaver (Poddubnaja- 

 Arnoldi, 1936), the individual branches continue their growth for an 

 appreciable period, although only one of them contains the vegeta- 

 tive nucleus. In Ulmus (Shattuck, 1905), Senecio, Crepis, and 

 Secale (Poddubnaja-Arnoldi, 1936) it degenerates even before the 

 pollen grains begin to germinate and does not enter the tube at all; 

 nevertheless the tube continues to function normally. 7 In Cheno- 

 podium, Atriplex, and Salsola it seems to break up and diffuse into 

 the surrounding cytoplasm (G. O. Cooper, 1935), and in Musa 

 (Juliano and Alcala, 1933) and Senecio (Poddubnaja-Arnoldi, 1933) 

 it fragments into small bits which seem to be quite functionless. 

 In some other plants also the vegetative nucleus assumes a very 

 abnormal appearance. For instance, in the pollen tubes of Viola 

 odorata (Madge, 1929) it becomes 4 times, in Cymbidium bicolor 

 (Swamy, 1941) 18 times, and in Vallisneria americana (Wylie, 1923) 

 27 times longer than broad. In a few members of the Labiatae 

 (Finn, 1939) and in Nicotiana (Goodspeed, 1947) the elongation is 

 sufficiently pronounced to give it a filamentous outline. 



On the basis of these and other data Poddubnaja-Arnoldi (1936) 

 regards the vegetative nucleus as a vestigial structure without any 

 important function in the growth of the pollen tube. This view is 



7 See Hewitt (1939) for other examples of an early degeneration of the vegetative 

 nucleus. 



