Ch. II] CHARACTERISTICS OP PLANTS 13 



nificance, from anceh^tral forms, as noted already under 

 HEREDITY. Third, plants are still in process of evolution, • 

 and hence, for causes and by methods still unknown, are con- 

 stantly developing new features called variations, or better, 

 — MUTATIONS. Fourth, the adaptations, the heredity, and 

 the mutations of plants are all more or less affected, and 

 even in some degree directed, by the chemical nature of the 

 materials they are composed of, and the physical forces playing 

 upon them from the world in which they live ; and on this 

 account many of their features have a purely incidental, or 

 mechanical, or, as we may designate them collectively, struc- 

 tural significance. Thus the actual plant embodies the 

 resultant of the simultaneous action upon it of adapta- 

 tional, hereditary, mutational, and structural, with some 

 other minor, factors. It is the task of the botanist to chs- 

 tinguish and separate the various influences which make the 

 plant what it is, for which purpose he needs above all an 

 open mind, a willingness to weigh all forms of evidence, and 

 freedom from the human hxii unscientific tendency to adopt 

 some single favorite viewpoint and explain all phenomena 

 therefrom. Many matters in science are interpreted dif- 

 ferently by equally competent investigators, but discussion 

 and further investigation always bring the truth, for the 

 recognition of which we have only one test, — it is that 

 upon which the great majority of competent investigators, 

 after full and disinterested investigation, agree. 



The generahzed statements of this chapter are intended 

 to enable the student to approach his study with better 

 understancHng. We turn now to the concrete facts and 

 phenomena of plant nature. 



