AND INHERITANCE IN PEDIASTRUM. 



415 



cell numbers produced by bipartition. The endless variations in 

 form found on comparing a series of colonies are the expression of 

 the unstable equilibrium, arising especially from the simultaneous 

 operation of the law of bipartition and the physical principle of 

 least surfaces. 



In the series of colonies chosen I have included as noted only 

 individuals with the common plan of i -f- 5 + lo, since it is im- 

 possible to compare the angles fairly in individuals with different 

 geometric plans. This is obvious in the case of the superficially 



Fig. 25. Pediastrnm Boryannm. Colony with cell number 6 so displaced 

 that the side which should be adjacent to cell 5 is in contact with cell i, the 

 side that should be in contact with cell i is in contact with cell 2, etc. The 

 remainder of the cells are normally placed. X about 600. 



rather regular colony numbered 67 (Fig. 25). In this colony all the 

 cells are regularly and symmetrically placed except No. 6, in series 

 11. This cell has swung around until its major axes, both radial 

 and tangential, are displaced about 45°. Its reentering angle nor- 

 mally under the middle of cell 16 is now under cell 15. The en- 

 tire cell has been, broadly speaking, rotated through one sixth of 

 its circumference so that each of its sides has been displaced by 

 one in its relations with the sides of the neighboring cells. The side 

 normally adjacent to cell 5 is now adjacent to cell i. The side 

 normally adjacent to cell i is now adjacent to cell 2 and much 

 reduced in length. The side normally adjacent to cell 2 is now 

 adjacent to cell 7, etc. Cells 15 and 7 have slipped in toward the 

 center of the colony so that its peripheral outline has been flattened 



