Progression, Retrogression and Degression. 67 
is without doubt the general rule. That an actual internal 
loss may also occur is probable on general grounds, but 
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. 1 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 afresh each time with any hope of success. 
The origin of svstematic and horticultural varieties 
1 On this point see also my Intracellulare Pangenesis, English 
translation by Prof. C. Stuart Gager (Chicago, The Open Court 
Publishing Co., 1910). 
