THE PILOBOLUS GUN AND ITS PROJECTILE 157 



of the glass there are five possible ways in which its two elements 

 may be arranged : (1) the drop of cell-sap may be directly in front 

 of the sporangium, so that the axis of the projectile is perpendicular 

 to the surface of the glass ; (2) the drop of cell-sap may be more or 

 less in front of the sporangium, so that the axis of the projectile is 

 inclined to the surface of the glass ; (3) the sporangium and the drop 

 of cell-sap may be side by side, so that they strike the glass simul- 

 taneously ; (4) the sporangium may be more or less in front of the 

 drop of cell-sap, so that the axis of the projectile is inclined to the 

 surface of the glass ; and (5) the sporangium may be directly in 

 front of the drop of cell-sap, so that the axis of the projectile is 

 perpendicular to the surface of the glass. All these possible arrange- 

 ments must now be considered and, for the sake of convenience, 

 they will be considered in the following order: (1) and (2), (4), 

 (3), and (5). 



(1) and (2). If the dro2J of cell-sap is either directly or more or 

 less in front of the sporangium, the drop will strike the surface of 

 the glass first, flatten out there, and so cause the sporangium, which 

 owing to adhesion cannot leave its surface, to take up a position at 

 or near its centre, so that the gelatinous side of the sporangium will 

 be turned toward the surface of the glass and the unwettable convex 

 side will be turned away from the surface of the glass and will project 

 freely into the air, as shown in Fig. 74, B. 



(4). If the sporangium is more or less in front of the drop of the 

 cell-sap, but not directly in front as in case (5), as shown in Fig. 74, A, 

 the sporangium will strike the surface of the glass first and a moment 

 of momentum about the point of first contact of the sporangium 

 with the glass (to which the arrow in Fig. 74, A, points) will rotate 

 the projectile (to the left in Fig. 74, A), with the result that the 

 drop of cell-sap will strike the surface of the glass, spread out owing 

 to the force of impact and, in spreading out, drag the sporangium 

 round by its adhesive wettable side at the same time pushing away 

 its non-adhesive unwettable side, thus forcing the sporangium to 

 take up a position at or near the centre of the drop with its gelatinous 

 under side toward the glass and still in contact with the water and 

 with its black convex side projecting into the air. 



(3). If the sjjora7igium and the drop of cell-sap strike the surface 



