302 



STRUCTURAL BOTANY 



down this distinction, for they have proved that in two 

 G-ymnospernis, at any rate, true motile spermatozoids 



are formed. The 

 plants in which 

 this important 

 discovery has 

 been made are 

 the Maidenhair 

 Tree (G-inkgo 

 biloba), a tree of 

 an ancient type, 

 usually referred 

 to the Coniferse, 

 and Cycas revo- 

 luta (see p. 35). 



FJG. 115. GinTcgo biloba. A, pair of generative 

 cells in the pollen-tube. On the outer side of 

 each cell a spiral coil is seen in connection with 

 the nucleus. B, generative cell, showing the 

 spiral spermatozoid in surface view, x 225. 

 From a preparation by Dr. Hirase. (R. S. ) 



In both these cases (to which others will no doubt be 

 added) a pollen-tube is formed, which enters the nucellus, 



as in other Gymno- 

 sperms, but does not 

 reach the archegonia. 

 Two generative cells 

 are formed in the usual 

 way, but each of these 

 gives rise to a large, 

 spirally-coiled sperma- 

 tozoid, with numerous 



FIG. UG.-Cycasrevoluta. Pair of genera- ^lia ( see Figs. 115 and 



tive cells from a pollen -tube, showing v . 



the spirally-coiled spermatozoids, sur- 116, which have been 



rounded by the protoplasm of the cell s k etcned from the 

 The hne stnation overlying the spiral 



coil indicates the cilia, x 190. From original preparations, 



a preparation by Prof. Ikeno. (R. S.) kindly gent by p rof 



Ikeno and Dr. Hirase). The spermatozoids break out 

 from the pollen -tube, and by their own active move- 



