136 



GYMNOSPERMS 



drop of strong sugar solution and still further protected by a bell jar, 

 the movements have continued for 5 hours. How much longer they 



Fig. 147. — Dioon edule: a reconstruction, from several sections, of an ovule at the 

 time of fertilization. The pollen tube on the left shows the body cell still undivided; the 

 one in the middle shows two sperms and the remains of the prothaliial and stalk cells; 

 the one on the right shows the two sperm mother-cells and the spiral ciliated band be- 

 ginning to develop. Two pollen tubes have discharged their sperms. A sperm has en- 

 tered the egg on the left; the one on the right still shows the ventral canal nucleus. Two 

 sperms, in the thick liquid discharged from the pollen tube just above them, are ready 

 to enter the egg. The dark line below the nucellus is the mcgaspore membrane. — After 

 Chamberlain.'"' 



would move under natural conditions is conjectural. Efforts to keep 

 the sperms alive after escaping from the pollen tube were not sue- 



