CLASSIFICATION. 65 



plant is greatly changed in general appearance, and 

 botanists call it a new species.^ 



Then, whatever was the orginal species of Eri'ca, 

 or Heath, which came to South-West Africa, it has 

 been probably long extinct ; but as its seeds became 

 scattered about and found different conditions in 

 different places, the plantlets grew up, altering their 

 features, and so gave rise, first to " varieties ; " then these 

 became "species," as the degrees of differences in- 

 creased which finally qualified them to become species. 

 It is a common thing to find South African species of 

 the many bulbous plants, as Orchids, etc., to be localized 

 in particular spots, probably where they were originally 

 evolved. 



On the other hand, the Bracken Fern {Pte'ris 

 aquili'na), common over all the slopes of the Table 

 Mountain range, is just like the English plant, and 

 does not appear to have varied here any more than 

 it has in Europe. 



So, too, Oxalis cer'nuct, as mentioned, is common in 

 various places all round the Mediterranean Sea; but 

 it is known to have been introduced about 1804, so 

 that after a hundred years or so it has never altered 

 in the least in the Northern regions. 



There is, in fact, no necessity for plants to change, 

 if their constitution can accommodate itself to the new 

 localities ; but if it cannot, it must die. 

 * See above, p. 64. 



F 



