SEED-BEARING PLANTS 405 



bumping against each other and the wall of the tube in 

 their reckless haste. They seldom escape from the upper 

 cut end of the pollen-tube, although they as frequently 

 swim toward this end of the tube as the other end, so far 

 as could be obsen.'ed. In many cases the poUen-tubes 

 were cut so that the spermatozoids escaped into the solu- 

 tion, and in numerous other cases mature turgid tubes 

 burst in the process of cutting, discharging the uninjured 

 spermatozoids in the sugar solution. The writer was 

 thus able in many cases to study the spermatozoids swim- 

 ming free and observe their unobstructed motion. 



"The motion of the spermatozoids when swimming free 

 in sugar solution is in no way different from their motion 

 when in the pollen-tube. The general motion is a con- 

 tinuous rotation of the body, always in the same direction, 

 around an axis passing through the apex of the helicoid 

 spiral. Mewed from the head end or apex of the spiral 

 the rotation is in the direction of the hands of a clock, and 

 contrary to the turns of the spiral band. They roU 

 around, first here, then there, resembhng in this respect 

 the motion of Pandorina. After moving about rapidly 

 for from five to fifteen minutes they usually cease all pro- 

 gressive motion, but continue to rotate for a considerably 

 longer period. The rotar\' motion also soon ceases, but the 

 cilia continue to \dbrate for a considreably longer time. 

 The spermatozoids of Zamia also have an amoeboid mo- 

 tion, which is particularly noticeable while they are in- 

 closed in the pollen-tube. The apex of the spiral as a 

 whole frequently rotates in a most remarkable way, 

 turning in a circle, pushing out first this way and then that 

 way with the greatest freedom of motion, as if selecting a 

 point of exit or ingress. In other cases the base or the side 



