THE REPRODUCTIVE STRUCTURES 



109 



microscopes, keep pace with the growth of the body cell 

 and finally reach a diameter of one one-thousandth of an 

 inch, so that they can be seen with an ordinary pocket 

 lens. In the earlier stages the body cell is elongated in 

 the direction of the long 

 axis of the pollen tube; 

 later the free end of 

 the pollen tube hang- 

 ing in the pollen cham- 

 ber becomes swollen, 

 and the body cell 

 gradually assumes a 

 nearly spherical shape 

 (Figs. 56 and 57). 

 While the change in 

 the shape of the body 

 cell is , taking place, 

 the blepharoplasts 

 rotate 90°, so that 

 their position becomes 

 transverse to the long 

 axis of the pollen tube. 

 The growth of the 

 pollen tube and of the 

 structures within it is 

 slow and steady up 

 to this point, but the 

 final stages, the division of the body cell and the forma- 

 tion of two extremely complicated sperms, take place 

 with astonishing rapidity. The two cells resulting from 

 the division of the body cell are shown in Fig. 58. 

 Within each of these cells a sperm is formed. 



Fig. 58. — Dioon edulc: end of pollen 

 tube, showing the two young sperms 

 resulting from the division of the body 

 cell. A beak of the nucleus has become 

 attached to the mass of granules derived 

 from the blepharoplast. This is the 

 beginning of the spiral band. Highly 

 magnified. 



