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CHAPTER VI. 
SPECIAL MORPHOLOGY AND CLASSIFICATION. 
Even the most superficial observation of the vegetable 
world is sufficient to show that no form exists on the earth 
as a single individual, but that each is repeated with 
. very slight variations. These variations, however, refer only 
to the size, colour, degree of hairiness, and other external 
character of the separate organs, to the number of branches,” 
leaves, and flowers, in short to points so unessential that 
the same name is naturally given to all these similar indi- 
viduals, Closely connected with this is the additional fact — 
that new individuals which spring from seeds resemble ex- . 
actly the individuals which produced the seeds, with the | 
exception again of slight and unimportant variations. The ~ | 
entire collection of those plants which thus coincide in all — 
essential characteristics, and of all those which are de- 
scended from the same parent, is called a Sfecies. But a 
species remains unchanged, even within the limits defined 
by essential characteristics, only as long as the vital con- 
ditions remain the same. When these are altered by’ | 
change of climate or food, or of relationship towards other 
organisms, whether man, animals, or other plants, even 
some of these characters gradually disappear, and are re- 
placed by others. A species is therefore only an assem- 
blage of forms which resemble one another for the time 
being, and is not a type rigidly defined by nature. 
Dependent on changes produced by cultivation, a species 
- 1s divided into Swd-species ; and when the characters are 
hereditarily transmitted with constancy through the seed, . 
into faces. Variations within the same race are called 
Varieties, and these again are divided into Sb-varteties. 
All species which agree in the essential characters of 
