GYMNOSPERMS. 155 



which is in contact with one end of the blepharoplast in the earlier 

 part of its development (Fig. 63, A). 



The mature spertnatozoid is also quite similar in structure to that of 

 Cycas, consisting of a large nucleus completely surrounded by a layer 

 of cytoplasm in which the ciliferous band, or blepharoplast, is located 

 just beneath the plasma membrane. The blepharoplast is in the form 

 of a helicoid spiral, making about five or six turns counter clock-wise 

 and embracing about one-half of the body of the cell (Fig. 65, B). 

 The spermatozoid, as in the ferns, is a transformation of the entire 

 cell and, therefore, a true spermatozoid. 



The development of the spermatozoid in Ginkgo according to Hirase 

 ('98) is quite similar to that in Cycas as described by Ikeno. In the 

 generative cell of Ginkgo Webber ('97) and Hirase ('98) find that, 

 when the nucleus becomes strongly flattened or lenticular, a large 

 nucleolus-like body appears on either side of the nucleus between the 

 nuclear membrane and the young blepharoplasts. Other similar but 

 smaller bodies are sometimes present in the cell. Accompanying these 

 two bodies Hirase finds coarsely granular cytoplasm. The bodies in 

 question react toward stains much as do nucleoli, and, since they dis- 

 appear at a later stage, it is probable that they represent merely extra- 

 nuclear nucleolar substance. 



Miyake ('02) finds that after the division of the generative cell in 

 Ginkgo a cell- wall is formed between the two daughter-cells, and that 

 a distinct and firm wall was always found around the two spermato- 

 zoids. The fact that a wall is or is not formed about the daughter- 

 cells, /. ., the mother-cells of the spermatozoids, does not affect the 

 morphological rank of the spermatozoid. 



The mature spermatozoid of Zamia is probably the largest male 

 gamete known in the plant kingdom, being plainly visible to the 

 unaided eye. When swimming freely and without pressure it is 

 slightly ovate, nearly round or compressed spherical (Fig. 65, B). 

 They vary greatly in size, however, ranging in length from 222 to 

 332 /i, and in width from 222 to 306 /*. 



Ikeno describes the spermatozoid of Cycas as being provided with 

 a tail which is merely the elongation of the posterior part of the cyto- 

 plasmic mantle. Measured in sections the length was found to be 160 p. 

 and the width 70 /z. The length of the tail was 80 jj. or equal to that 

 of the body. Fujii has shown that the tail attributed to the spermato- 

 zoid of Ginkgo was an artifact, and this statement has been confirmed 

 by Miyake. Since no tail exists in Zamia, it is probable that that 

 described for Cycas may also have been the result of abnormal 

 conditions. 



