232 baker's north YORKSHIRE. 



plants, Mercurialis annua and Galactites tonientosa. So that, 

 in respect of citizenship, we have five categories to separate the 

 species amongst, viz. : — 



I. The Natives, so far as we can now judge, the aboriginal 

 possessors of the soil. 



2 and 3. The Colonists and Denizens, the well-established 

 importations of the Historic period. 



4. The Aliens, importations not fully established. 



5. The Incognita, species to be rejected from the list, either 

 as being extinct, or as requiring confirmation before they can be 

 claimed with safety. 



The Stational Range of Species. — In treating of the distribution 

 of species we have in the first place to consider the familiar 

 facts as to what is called station or habitat. Amongst plants 

 we all know that one affects woods and shaded places, 

 another dry banks and wall tops, a third pastures and grassy 

 commons, a fourth bogs and ditches, a fifth heaths, a sixth 

 marshes by the sea-side and the vicinity of salt springs inland, 

 a seventh cultivated fields and waste ground : some species 

 being restricted, with but trifling exception, to one of these kinds 

 of locality, others growing as if indifferently in tv/o or three of 

 the kinds, whilst others are to be met with habitually in several 

 or almost all of them. Each species plainly has its own special 

 power of adaptation to varied physical conditions, and that power 

 is very different in different natural orders, different genera, and 

 even often in different species of the same genus. It is the 

 power of adaptation possessed by the plant which the geographical 

 botanist has to deal with when he comes to consider it, just as 

 the physiologist has to deal with its structure and the functions 

 of its various organs, and the describer of species and systematist 

 has to deal with its diagnostic characters. So much light or 

 shade, such a kind of soil, so much heat, so much moisture, 

 such a degree of consistency of soil 3 in regard to all these points 

 each species has its own special constitution, and this must be 

 provided for in every one of its stations in order to enable it to 



