220 THE EVOLUTION OF CONTINUITY 



surface. This would happen when the organism was less 

 dense than the water. It would be indirect repulsion, a 

 matter of displacement by the more strongly attracted 

 water. 



Gravity acts in the same three ways when the atmos- 

 phere is aerial and not watery. 



The natural effect of Gravity being to keep an organism 

 at rest in a fixed position, we may conclude that the question 

 of an organism's being fixed or motile in character will be 

 determined fundamentally by the manner and degree in 

 which it is acted on by competing attraction-forces ; for 

 all movement, except such as is towards the earth, takes 

 place in spite of the direct action of Gravity. 



Living organisms may be divided into the motile and 

 the non-motile ; that is, such as have the power of moving 

 from place to place, and such as remain fixed in position. 

 It is unnecessary to point out that the increase in bulk 

 accompanying growth involves movement, though in no 

 way connected with motility. It is, so to speak, a movement 

 of extension, and may be horizontal or vertical in its direc- 

 tion, or at any angle from the perpendicular. 



The plan on which bulk increases varies according to 

 the Continuity the growing organism exhibits, and it is 

 when this is serial in nature, and growth takes the form of 

 linear extension, that the movement of growth is most 

 detectable. This serial extension, especially if in an upward 

 direction away from the surface of the earth, indicates a 

 certain degree of successful competition by some force acting 

 in an opposite direction to the direct force of Gravity. The 

 competing force may be Gravity itself acting indirectly as 

 a repellent, causing the growing organism to pull upwards 

 more or less as a string of corks would do if fastened by one 

 end to the bed of a pond, and as exemplified by certain 

 sea-weeds and hydrozoal colonies. It may be that the 

 little air-floats of the bladder-wrack originated through 

 Gravity, gases from all parts of the growing " plant " 

 having percolated upwards in the direction of the surface 

 of the water to form little imprisoned collections in terminal 

 situations. 



But it is very probable that in the origination, and 

 maintenance, of serial growth away from the earth a force 



