195 



i anirnak in comparison with that of the living 

 <>t later periods of evolution. Indeed, aid r what we have seen in 

 tin- la-t ehapter, in non-living nature then eem- to be ratl, 

 o|ij)ositely directed tendency, a drift towards the highest degree of 

 >ymmetry possible .The cases of apparent and mimetie ^vmi. 

 dealt with in the above may serve to sustain this view; further the 

 tact that polymorphic substances generally change into higher 

 "A'mmetrical forms, when teinj>erature increases. In the next eh.ipt. i 

 we shall obtain yet more evidence for this view: we shall see. that 

 optical antipodes, possessing only symmetry-properties of the tii-t 

 order, have a natural tendency to pass into optical inactive systems 

 exhibiting symmetry-properties of the second order also. A certain 

 tendency to form the more symmetrically built molecules in cases, 

 where several isomerides may occur simultaneously, is observed 

 on many occasions by chemists also, and it is a well-known fact for 

 instance, how easily the threefold symmetrically substituted deri- 

 vatives of phenoles, aniline, etc. are commonly produced, in compari- 

 son with their less symmetrical isomerides. 



On the contrary, evolution in living nature seems to proceed in 

 exactly the opposite direction, the lower animals showing in many 

 cases a much higher symmetiy than the mere bilateral one of the 

 animals, which have appeared in the later periods of the earth's 

 history. A certain preference for pentagonal symmetry, both in the 

 case of animals and of plants, seems to exist even here, a symmetry 

 so closely related to the important ratio of the "golden section," 

 .and unknown in the world of inanimate matter. 



The view, that really the older forms should possess the higher 

 symmetries, is probably also sustained by the remarkable phenomena 

 of the occurrence of so-called peloria l ) in flowers. 



It has been observed for a long time that many plants, the flowers 

 of which have only bilateral symmetry, suddenly produce at the top 

 of an inflorescence a flower which jhows the perfect symmetry of 

 one of the axial groups, or of the groups C* . Thus Delphinium pere- 

 grinum produces occasionally a completely pentagonal blossom; 

 the common fox-glove (Digitalis purpnrea monstrosa) exhibits tin- 

 same phenomenon (fig. 156), as the accompanying figure (after 

 H. De Vries) clearly shows. Among Orchidaceae the species Cattlcya 

 marginata and Phalaenopsis Schilleriana occasionally show a pelo- 



l) From : Triiwp = monstrnni. 



