464 Plant Physiology 



characteristics of parents are transmitted to the offspring, 

 yet not all individual characteristics of all ancestors are 

 transmitted. The offspring may exhibit modification. 

 This modification may be evident under constant condi- 

 tions, or it may occur in response to environmental changes. 

 It may be an acquirement manifest merely during the 

 life of the organism, or it may be innate and trans- 

 missible. Every organism possesses an individuality. 



281. Individuals and species. - - Individuals which re- 

 semble one another closely and which have a common 

 origin may collectively constitute what may be called a 

 race, variety, or species. Our ideas of such groups are 

 based upon a study of individuals (few or many, small or 

 large populations) and naturally center about average 

 examples. We recognize, however, certain extremes ; in 

 fact, there are multitudinous variations, for there may be 

 as many extremes as characters, or character combinations. 

 These extremes, perhaps, have in many cases so insensibly 

 entered into other recognized varieties that opinions would 

 differ in determining to which variety a particular individual 

 should be attached. Some varieties, on the other hand, 

 may stand apart with sharply differentiated characters; 

 within these, individuals may also differ perceptibly 

 among themselves. In any case, a group of individuals, 

 such as a race, variety, or species, is in a measure a theo- 

 retical average with respect to characters, and is made 

 up of a series of individuals showing in the different 

 characters considerable fluctuation. 1 



1 All organisms resembling one another closely must look alike to 

 the inexperienced eye, - - to the eye unfamiliar with the group. Upon 

 close inspection and measurement, however, relatively wide differences 



