170 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



supported by Suita (1936, 1937a, b), who studied the pollen grains 

 of Crinum with the Feulgen method. He states that soon after its 

 formation the vegetative nucleus increases in size and becomes 

 amoeboid. Later it begins to stain very faintly, indicating a de- 

 composition of the chromatin. He agrees, therefore, that it is a 

 degenerating structure without any important function in the life 

 of the pollen tube. 



While further evidence would be welcome, it seems safe to con- 

 clude that the old view attributing a leading role to the vegetative 

 nucleus in the growth and direction of the pollen tube now needs 

 modification. It is likely that these functions are really discharged 

 by the nucleus of the generative cell itself and later by the nuclei 

 of the two male cells formed by its division. 



Development of Pollen in the Cyperaceae. The course of de- 

 velopment described above is generally characteristic of all angio- 

 sperms, dicotyledons as well as monocotyledons, the family Cy- 

 peraceae being the only notable exception. Juel (1900), Stout 

 (1912), Piech (1928) and others have shown that, of the four micro- 

 spore nuclei produced after meiosis, only one develops further, while 

 the other three become pushed toward one end of the mother cell 

 (Fig. 104 A, J5). The functional nucleus, which lies in the center, 

 divides with its spindle oriented in the direction of the long axis of 

 the cell (Fig. 104(7, D). The cell plate, which is laid down between 

 the vegetative nucleus and generative nucleus, extends around the 

 latter so as to give rise to a continuous plasma membrane. The 

 generative cell (Fig. 104Z?) soon becomes spindle-shaped and divides 

 to form the two sperm cells (Fig. 104jP). 



A few doubtful points, which need further clarification, are the 

 following: (1) whether the functioning microspore nucleus is sepa- 

 rated from the three nonfunctioning nuclei by a wall, (2) whether 

 the nonfunctioning nuclei are separated from one another by walls, 

 and (3) what the fate of the nonfunctioning nuclei may be. Tanaka 

 (1940, 1941), who has recently discussed these questions, believes 

 that normally a plasma membrane separates the functioning micro- 

 spore nucleus from the three nonfunctioning nuclei and that subse- 

 quently similar membranes arise between the latter. The non- 

 functioning nuclei sometimes undergo one division, resulting in a 

 pair of daughter nuclei in each of the three cells. No separating 

 wall is formed between them, however, and they are soon absorbed. 



