Progression, Retrogression and Degression. 67 



is without doubt the general rule. That an actual internal 

 loss may also occur is probable on general grounds, Init 

 very difficult to demonstrate in a given case. For every 

 positive result points to latency, and nothing but a nega- 

 tive result after exhaustive investigation could warrant 

 the conclusion that a character had absolutely disap- 

 peared. 



The multiformity of species within the larger groups 

 is also due to a phenomenon which Darwin calls parallel 

 variation. I refer to the repeated appearance of the 

 same new character in related or remote groups.^ Climb- 

 ing and tendril-bearing plants, parasites, saprophytes 

 and insectivorous plants, decussate phyllotaxy, are a few 

 names from a vast number of instances. One of the 

 greatest difficulties for the systematist, the question as to 

 the mono- or polyphyletic origin of many characters is 

 a problem of a similar nature. For example, are the 

 siliqua and silicula in the Cruci ferae, or is the position 

 of their embryo to be regarded as an indication of mono- 

 or polyphyletic origin? Do the Sympetalae with an in- 

 ferior ovary originate from other Sympetalae or from 

 epigynous Choripetalae ? Have the Gymnosperms arisen 

 once or oftener from the vascular Cryptogams? We do 

 not know, because, on such points, the highest authorities 

 are not in agreement. And so long as these differences 

 of opinion exist it will be difficult to approach the question 

 as to the cause of the parallel formation of specific char- 

 acters — whether they arise from a common latent source, 

 or afresli each time — with any hope of success. 



The origin of svstematic and horticultural varieties 



^ On this point see also my IntraccUularc Pangenesis. English 

 translation hy Prof. C. Stuart Gagcr (Chicago, The Open Court 

 Publishing Co., 1910). 



