Mar. 1901.] BOTANICAL SOCIETY OF EDINBURGH 53 



If the biomolecules resulting from dedoublemcnt are 

 like each other, but unlike the primitive biomolecule, the 

 development is homogenetic, and is figured as under — 

 a' . . b' . . c' . . d' . . M' = e' + c' 



After further assimilation, / and / may each undergo 

 dt'douUenient into two biomolecules which will be identical 

 to a\ In this case the evolutionary biomolecular cycle is 

 composed of at least two homogenetic developments ; of 

 course there may be more until the primitive mother 

 molecule is reproduced. In homogenetic development 

 multiplication and reproduction are two distinct pheno- 

 mena, and are accomplished at different times. In the 

 simplest case, where the cycle is composed of two 

 developments, reproduction only occurs at the second 

 dMouUcment, where the primitive molecule is quadrupled ; 

 while multiplication of molecules (but not reproduction of 

 the original) occurs at the first dedouhlement. Two phases 

 are thus to be distinguished in homogenetic development — 

 (1) a period of multiplication, extending from the first to 

 the last development ; (2) a period of reproduction, in which 

 only the last development is concerned. Multiplication 

 (duplication of the number of molecules) is thus to be care- 

 fully distinguished from reproduction (regeneration of the 

 original molecule). The two phenomena are not necessarily 

 concomitant. 



When the biomolecules resulting from (UdouUement are 

 unlike each other, and also unlike the primitive biomolcule, 

 the development is hcterogenetic. Thus — 



a" . . h" . . c" . . d" . . M" = e" + i" 



e", after further assimilation, may undergo dddoublcment, 

 producing two biomolecules, a" ci" , identical to the primitive 

 one ; while i , although it undergoes further development 

 and dedouhlement, never regenerates a". 



This development is the easiest, and by far the com- 

 monest, in nature. The vital cycle is composed of at least 

 two developments, but two kinds of molecules must be 

 distinguished, some able to regenerate the primitive 

 biomolecule after a more or less long series of develop- 

 ments, the others devoid of this faculty. The former are 

 genetic, the latter somatic biomolecules. The former alone 



