718 Fluctuations 



bility falls under two heads. They obey quite 

 the same laws and are therefore easily confused, 

 but with respect to questions of heredity they 

 should be carefully separated. They are des- 

 ignated by the terms individual and partial 

 fluctuation. Individual variability indicates 

 the differences between individuals, while 

 partial variability is limited to the devia- 

 tions shown by the parts of one organ- 

 ism from the average structure. The same 

 qualities in some cases vary individually and in 

 others partially. Even stature, which is as 

 markedlv individual for annual and biennial 

 plants as it is for man, becomes partially variant 

 in the case of perennial herbs with numbers of 

 stems. Often a character is only developed once 

 in the whole course of evolution, as for instance, 

 the degree of connation of the seed-leaves in 

 tricotyls and in numerous cases it is impos- 

 sible to tell whether a character is individual or 

 partial. Consequently such minute details 

 are generally considered to have no real im- 

 portance for the hereditary transmission of the 

 character under discussion. 



Fluctuations are observed to take place only 

 in two directions. The quality may increase or 

 decrease, but is not seen to varv in anv other 

 way. This rule is now widely established by 

 numerous investigations, and is fundamental to 



