I30 



GYMNOSPERMS 



blepharoplasts appear. They are at the side of the nucleus opposite 

 the prothallial cell, and one of them soon moves around to the oppo- 

 site side of the nucleus. They remain in this position and grow rapid- 

 ly. As the elongated body cell increases in size, it gradually becomes 

 spherical, and the two blepharoplasts move 90 degrees, so that a 

 line drawn through them would be perpendicular to the long axis of 

 the pollen tube (figs. 138, 139). The blepharoplasts are at first very 



/3a 



Figs. 138 and 139. — Dioon edule: fig. 138, December material, body cell elongated 

 and blepharoplast parallel with the long axis of the pollen tube; fig. 139, May material 

 with blepharoplasts rotated until they have become transverse to the long a.xis of the 

 pollen tube; X237. — From Chamberlain, The Living Cycads"° (University of Chicago 

 Press). 



dense and homogeneous, but later become very vacuolate and reach 

 an immense size, from 16 to 18 microns in diameter in Dioon edule, 

 and 20-27 microns in Ceratozamia mexicana, the largest yet known. 



The radiations surrounding the blepharoplasts are very conspicu- 

 ous and often extend to the wall of the cell. 



Shortly before fertilization the body cell divides, and in each of the 

 two resulting cells a single sperm is developed. As the sperm grows, 

 the radiations begin to disappear and the blepharoplast breaks up 

 into a great number of small granules (fig. 140). Some of these be- 

 come attached to a beaklike protuberance of the nucleus, which in- 

 creases immensely in size and rotates so that the mass of granules, 



