304 



STRUCTURAL BOTANY 



down this distinction, for they proved that in some 

 Gymiiosperms true motile spermatozoids are formed. 



The plants in 

 which this im- 

 portant discovery 

 was first made are 

 the Maidenhair 

 Tree (Ginkgo 

 biloba), a tree of 

 an ancient type, 

 nearly related 



FIG. ll8.-Ginl-go Ulola. K pair of generative Ponifpr-P 



cells in the pollen-tube. On the outer side of to tne T6, 



each cell a spiral coil is seen in connection with an( j (Jvcas TCVO- 



the nucleus. B, generative cell, showing the 



spiral spermatozoid in surface view, x 225. iUta (S66 p. 60). 



From a preparation by Dr. Hirase. (R. S.) j n both these 



cases (to which others have now been added) a pollen-tube 

 is formed, which enters the nucellus, but does not reach the 



archegonia, and serves 

 chiefly to anchor the 

 pollen - grain in the 

 right position. Two 

 ^generative cells are 

 formed in the usual way, 

 but each of these gives 

 rise to a large, spirally- 

 coiled spermatozoid, 



FIG. 119. Cycas revoluta. Pair of genera- w ^h numerous cilia 



tive cells from a pollen-tube, showing iio r ^ i 1 Q 



the spirally - coiled spermatozoids, sur- (see rlgS. llo and. Lly, 



have been 



rounded by the protoplasm of the cell, 

 The fine striation overlying the spiral 

 coil indicates the cilia. x 190. From sketched tromtheongl- 



a preparation by Prof. Ikeno. (R. S.) na i preparations, kindly 

 sent by Prof. Ikeno and Dr. Hirase). The spermatozoids 

 break out from the pollen-tube, and by their own active 



