220 SEMI-CENTENNIAL OF TORREY BOTANICAL CLUB 
providing for the stimuli. It is obvious that the mere molecular 
pulls involved in least surface phenomena could never lead directly 
to such violent changes of group relations, though they may be 
of final importance in determining the exact contours of the ring 
when once it is blocked out, as it were, as a result of the inter- 
cellular reactions which control the earlier swarming movements. 
It is then by no means enough, even when, as here, the in- 
herited cell form is not especially involved, to identify offhand 
the results of these complex physiological reactions as simply 
the expression of the physical principle of least surfaces which, 
at least as at present stated, is based on intermolecular relations. 
If the facts are as indicated we perhaps have here in the relations 
of the complex reactions of these simple organisms to the wide- 
Fics. 8,9,and 10. Pediastrum simplex Meyen, of the form known as Р. Siurmii 
Reinsch. 8, with small intercellular spaces, X about 200. 9, with a large inter- 
cellular space, X about 250. 10, sixteen-celled colony, eleven cells empty, simplex 
type, and five cells about ready to form swarmspores, Sturmii type, X about 200. 
spread symmetries of form, rounded contour, etc., which are based 
on the physical principle of least surfaces, a suggestion at least as 
to the origin of the so-called aesthetic satisfaction of higher 
organisms in physical symmetry and balance of configuration or 
artistic composition. This capacity to react to inequalities in 
contacts and pressures or unbalanced pressures from the environ- 
ment might be ascribed to a sense of symmetry and classed as one 
of the fundamental properties of living cells. "These ring-shaped 
colonies of P. simplex certainly suggest a notable delicacy of 
response to pressure and contact stimuli. 
еи Sturmii Reinsch, characterized by plumper, more 
р 1pposed to be solid instead of hollow, may 
