68 TRANSACTIONS OF THE [Sess. lxxvi. 



of the inflorescences of Ambrosia. At the same time, the 

 case dealt with here illustrates once again the phenomenon 

 to which the author has frequently made reference ; namely, 

 that our phylogenetic series, so far as we can depict them 

 with any degree of probability, all represent a reduction- 

 series. 



The following may be advanced in support of this : — 



1. In a descending series we have a definite starting-point 



(that is, some one of the more completely equipped 

 forms as distinct from the more reduced ones) with 

 which we can compare the less completely equipped 

 members of the series. 



2. In many instances the organs in question may still be 



recognised as rudiments. 



3. The descending series arise latest ; hence they are more 



completely preserved and easier to recognise than the 

 ascending with a history extending much further 

 back, and whose members are as a rule very in- 

 completely preserved. 

 Descending series of this kind are known to every 

 botanist, since they appear again and again in almost 

 every family. Other facts also indicate that organisms 

 become modified mainly through retrogression and simpli- 

 fication : thus " mutations," for example, are essentially 

 of this nature, since in them there is a loss of some definite 

 characteristic. 1 



Has then the "nisus formatoris" of the ancient philo- 

 sophers itself become antiquated ? Not at all ; botany at 

 least has remained youthful. To be convinced of this, one 

 need only glance at what is only possible where youthful 

 aspirations exist, namely, the construction of genealogical 

 trees from below upwards. " Alas, alike in their tenure of 

 life, they are mostly ruins, not of the trees, however, but of 

 the ephemeral day-flies ! " 



1 E. Baur, " Einfuhrung in die experimentelle Vererbungslehre " 

 (Berlin, 1911), says : "The large majority of mutations which have been 

 closely investigated depend simply on the loss of some single Mendelian 

 unit character. I have not found up till now, any absolutely certain 

 case in which one or more unit characters have arisen de novo." 



Munich, April 1912. 



