THE MALE GAMETOPHYTE 



4S7 



are difficult to find and are temporary structures without any special 

 significance. On the other hand, very distinct cell plates have been 

 figured in Lilium regale (Cooper, 1936) (Fig. 102/) and a number of 

 other plants, and their occurrence has also been confirmed from 

 studies on living pollen tubes of Crinum hildebrandtii (Kostriukova, 

 1939a), Lilium martagon (Kostriukova, 19396), and Narcissus 

 poeticus (Kostriukova and Benetskaia, 1939). 



In an important and extensive work on pollen tubes, Johnston 

 (1941) suggests that the inability to see cell plates is to be attributed 



A 





1 



Fig. 103. Division of generative cell in Eschscholtzia californica. {After Beatty, 

 1943.) 



to the exclusive use of nuclear stains in most studies of this type. 

 The same explanation holds good for the frequently reported absence 

 of spindle fibers in the division of the generative cell. Delafield's 

 haematoxylin, he says, is much superior to Heidenhain's haemato- 

 xylin for such purposes and should always be used for comparison. 

 As far as present evidence goes, it may therefore be concluded 

 that the division of the generative cell, whether it takes place in 

 the pollen grain or in the pollen tube, occurs in a fairly regular 

 fashion. However, in cases in which the tube is very narrow and 

 the chromosomes are rather large, there may be some disturbance 

 of the metaphasic alignment, resulting in their crowding or buckling. 

 It is also probable that the metaphase stage, owing to its very short 



