PLANT CLASSIFICATION. 43 



After spontaneous generation the automatic phylo- 

 genetic evolution begins and advances constantly. 

 Consequently the phylogenetic line rises from time to 

 time to higher stages of organization and division of 

 labor, but dies of old age if the automatic perfecting 

 process ceases. The phylogenetic lines of organ- 

 isms now living have therefore an unequal age; 

 those of the most highly developed plants and animals 

 had their origin in the earliest periods of organic 

 life, those of the lowest organisms in the most recent 

 periods. Hence no general genetic relation exists 

 among lines now living; only those that are nearly 

 related and have reached approximately equal stages 

 of organization may be regarded as branches of the 

 same phylogenetic stock. A phylogenetic plant sys- 

 tem does not exist in fact, but only in figure. 



If genetic relation between two races is assumed, 

 either as a reality or as a symbol, the degree of 

 relationship is determined in a theoretically exact 

 manner by the number and length of the phylo- 

 genetic steps which are found either between them 

 both or between them and the common starting 

 point, according as races belong to the same or 

 collateral lines. The fact that two organisms belong 

 to the same line of descent is recognized from the 

 ontogeny of the higher including the ontogeny of 

 the lower. 



Since only a proportionately small number of 

 known forms can appear as types of the supposed 



