THE MALE GAMETOPHYTE 165 



grains a definite cell plate was laid down in the beginning, but it 

 soon faded away, leaving the final separation of the sperms to a 

 constriction furrow which arose soon afterwards. In others the cell 

 plate persisted, and the progress of the constriction furrow was 

 arrested in this region although evident on either side of it; here the 

 splitting of the cell plate divided the generative cell before the 

 constriction could make much progress. 



It has proved more difficult to understand the mechanism of the 

 division when it occurs in the pollen tube. The chief points in 

 question are: (1) whether a regular metaphase plate is formed during 

 the division, (2) whether spindle fibers are present or absent, and 

 (3) whether cytokinesis takes place by constriction or by cell-plate 

 formation. 



Nawaschin (1910), O'Mara (1933), Wulff and Raghavan (1937), 

 Raghavan et al. (1939), and several other workers failed to find any 

 regular metaphase plates in the plants studied by them, viz., Lilium 

 martagon, L. regale, Nemophila insignis, and Impatiens balsamina. 

 On the other hand, Cooper (1936) reported their occurrence to be 

 a regular feature in Lilium regale, L. auratum, and L. philippinense 

 (Fig. 102), and believes that O'Mara's (1933) figures of an "irregular 

 metaphase" really represent a late prophase, the true metaphase 

 having been missed by him. Upcott (1936) and Madge (1936) 

 also found a metaphase plate in Tulipa and Hedychium respectively, 

 the only important difference being its oblique orientation which 

 gives more space to the chromosomes for their proper alignment. 

 More recently, well-differentiated metaphase plates have been re- 

 corded in Eichhornia (Banerji and Gangulee, 1937), Tulipa, Amar- 

 yllis, Nicotiana, Forsythia, Camellia, Bryophyllum (Johnston, 1941), 

 and Eschscholtzia (Beatty, 1943) (Fig. 103). 



Regarding the presence or absence of spindle fibers, Nawaschin 

 (1909) in Lilium martagon, Welsford (1914) in L. auratum and 

 L. martagon, O'Mara (1933) in L. regale, Trankowsky (1931) in 

 Convallaria majalis and Galanthus nivalis, Fuchs (1936) in Elaeag- 

 nus angustifolius , Wunderlich (1937) in Muscari racemosum and 

 M. comosum, Finn (1939) in Phlomis tuberosa, Raghavan et al. 

 (1939) in Impatiens balsamina, and several other workers failed to 

 find a spindle. On the other hand, Trankowsky (1931) in Hemero- 

 callis fulva, Cooper (1936) in Lilium auratum, L. regale, and L. 

 philippinense (Fig. 102), Madge (1936) in Hedychium gardnerianum, 



