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In order to determine whether particular groups of plants 

 found wild are to be considered as species, sub-species, races, 

 or varieties, a knowledge of the life-history, as well as of the 

 appearance of the seasonal forms of individual plants, and of 

 the kind and amount of variation which may occur among the 

 immediate offspring of one and the same individual, growing 

 under different conditions, is essential. It is, however, as a 

 rule, impossible to ascertain with certainty the parent of a 

 plant found wild, and very few species have been experiment- 

 ally cultivated with the object of recording the variation 

 exhibited by them. The systematic botanist, therefore, must 

 rely for his determinations mainly on morphological char- 

 acters, coupled with his knowledge of the development and 

 variation of the few forms which have be*en studied. 



His conclusions are, consequently, liable to error and to 

 correction in the light of subsequent research, while, in the 

 present state of our knowledge, there is obviously room for 

 considerable difference of opinion as to the kind of characters 

 and the amount of variation which should be held sufficiently 

 important to constitute an inter-specific gap, in consequence 

 of which plants which are regarded by some botanists as 

 distinct species are considered to be varieties by others. 

 The discovery of intermediate forms, also, sometimes leads 

 to two groups of plants, hitherto considered distinct, being 

 combined as one species, it being possible, in such a case, to 

 arrange a complete series of individuals between which there are 

 no marked differences, the slight differences noticed being such 

 as might be expected to occur in the offspring of one individual. 

 In defining the limits of the larger natural groups and 

 in deciding which species are to be included in the same 

 genus, which genera in the same order, and so on. there 

 is even more room for difference of opinion, and it must be 

 remembered that the difference is not so much as regards 

 facts, such as, for instance, the existence of certain characters, 

 but rather as regards decisions on such questions as to whether 

 the possession of certain characters in common by several 

 plants, may, or may not, be considered to prove a relationship 

 between them, and as to the degree of such relationship. It 

 will thus be seen that the Natural System of Classification is, 

 as yet, by no means perfect, and is liable to modification and 

 alteration as our knowledge extends. 



