202 



stem or in the centre of an inflorescence, and the changed flower has, 

 moreover, a tendency to take a more upright direction of growth 

 than is usual for it. (Antirrhinum maius', Digitalis; etc.). When such 

 an irregular blossom becomes symmetrical, this may occur in two 

 different ways : either the development of such parts which determine 

 the lack of symmetry in the ordinary individuals is stopped, or the 

 irregular parts are produced in greater number, so that a higher 

 symmetrical complex is the final result. In the first case it is said 

 that a "regular pelorium" is produced, in the latter case an "irregu- 

 lar" one. 



The regular pelorium is, therefore, a product of stagnation in the 

 natural development of the blossom, the irregular pelorium is the 

 result of an excessive development of certain parts of it. 



At present the phenomenon is generally explained in both cases 

 as a retrogression towards an older prototype. According to this 

 view, the occurrence of peloria is a case of atavism, of typical re- 

 trograde mutation. The irregular or less symmetrical flower is the 

 descendant of a higher symmetrical ancestor; and also here the older 

 form, therefore, appears to be that of higher symmetry. 



Indeed, it can hardly be denied that there is a sharp line of 

 demarcation between the forms of non-living and living nature 

 with respect to the part the principle of symmetry takes therein: 

 here the gradual evolution of forms from higher towards lower sym- 

 metry, and the characteristic preference for the irrational ratio of 

 the "aurea sectio"; there the tendency towards higher symmetry 

 as to a condition of greater mechanical stability, and the exclusion 

 of all irrational ratios in the periods of the symmetry-axes 1 ). There 



1 ) Also in chemical synthesis something of this kind is often observed. Thus 

 from glycol-iodo-hydrine and zinc-dimethyl not the primary propy I- alcohol, but the 

 more symmetrically built isopropyl-alcohol is formed, and the same occurs, if nitrous 

 acid acts upon normal propyl-amine. On dehydrating isobutyl-alcohol, not the 

 unsymmetrically built dimethyl-ethylene, but the more symmetrical isomeride is 

 formed. The same compound is produced, if sodium acts upon a mixture of methyl- 

 and allyl-iodide, and in greater quantity than the unsymmetrical hydrocarbon, if 

 zinc-methyl acts upon allyl-iodide. 



E. Krause and M. Schmitz (Ber. d. d. Chem. Ges., 52, 2150, (1919)) observed 

 in the case of symmetrically and unsymmetrically substituted #ry/-derivatives 

 of the metals stannum and lead remarkable differences in chemical behaviour 

 between the symmetrical and the unsymmetrical compounds. The influence of 

 the special symmetry of the molecule on its chemical properties is sufficiently 

 clear in these cases. Moreover, that a tendency towards the formation of symme- 



