and Laboratory Methods. 



17 



Fig. 4. — Generative cell 

 just dividing, the bleph- 

 aroplasts being found 

 in both poles of the cell. 

 X 260. — After Hirase. 



Fig. 3. — Slightly diagramatic 

 view of a living pollen-tube, 

 showng the generative cell 

 with fusiform nucleus («), 

 and the blepharoplasts (d) ; 

 about X 140. 



nucellus and the archegonia, with the grain-end turned toward the neck of the 

 latter (Fig. 6). 



The nucleus of the generative cell divides at right angles to the axis of the 

 pollen-tube, and after this division the whole cell is 

 divided into two equal cells without a wall between 

 them (Fig. 5). Two small dot-like bodies, the bleph- 

 aroplasts, which appear early in the generative cell 

 and during division, are found in both ends of the 

 cell, a small distance from the apex of the spindle, 

 and develop later into a spiral band with numerous 

 cilia (Figs. 2-5). In the living generative cell, 



these bodies are seen as 



refractive specks on both 



sides of the nucleus (Fig. 



3), although no radial stria- 



tions are visible, as was ob- 

 served in fixed material and 



described by Mr. Hirase 



(Figs. 2D, 4, 5). 



The whole contents of 



the generative cell is trans- 

 formed into two spermatozoids. After the sper- 

 matozoids are formed, the cilia on their bodies 

 begin to vibrate and presently the whole body 

 makes a motion, sometimes entirely changing its 

 position, within the common wall of the mother 

 cell (Figs. 7, 8). The presence of this cell-wall 

 has not been mentioned by Mr. Hirase, and the 

 fact was first proved by Mr. Fujii and myself. 

 It is interesting to note that this wall has not 

 been found either in Cycas or Zaniia. 



The correctness of our observations was 

 questioned by Dr. Webber in his recent paper. 

 He says : " Fujii's figure 2 seems to illustrate 

 exactly the same appearance as that described 

 above as occurring in Zamia, when the sperma- 

 tozoids pull away from each other and round up 

 so that they occupy less space, and have their 

 original location marked by the surrounding 

 plasma membrane of the pollen-tube. The writer 

 believes that it may be safely concluded that 

 Ginkgo corresponds with Zamia and Cycas in the 

 metamorphosis of the entire cell, and as stated 

 above, believes that this method of differentiation 

 is in harmony with what is found in Marsilia, 

 and probably in other ferns and lower plants." 

 But I am unable to accept his interpretation, as a 



Fig. .5. — Mature pollen-tube show- 

 ing its branched tip, the genera- 

 tive cell being already divided 

 into two cells which form the 

 spermatozoids ; x 120. — After 

 Hirase. 



