60 II. PERMANENCE OF SrECIES. 



here express by the term ' central tj^pe.' The central 

 type will be nearly synonymous with the proper meta- 

 physical notion of a species, apart from its varieties. It 

 is usually this same central type which is described in the 

 specific character of a plant ; although occasionally au- 

 thors endeavour so to frame their specific characters, that 

 these shall include all varieties of the species as well as 

 the central type. 



" Individual plants which differ from the central t3'pe 

 are named ' varieties.' Among varieties we may include 

 all the plants which are marked by any obvious difference, 

 ranging from the more trifling variations of colour and 

 size, to those which are so wide as to raise a question 

 whether the plants really belong to the same central tyj)e 

 or species. 



" Varieties appear to be less permanent than the cen- 

 tral tj'pes from which they originate. A tendency to 

 change again is usually observed in the descendants of 

 such varieties ; and the further change is frequently in a 

 reversed direction, or back towards the central type. 

 Among plants in a wild state, the tendency to keej) or to 

 resume the central type commonly seems to be gi'eater 

 than the tendency to vary from it. Hence there is an 

 appearance of permanence in species, as though each 

 kind had a limit to its power of change, beyond which its 

 descendants can never pass in a direction aberrant from 

 the central type, and from which limit there is a tendency 

 to return to that type. 



" But all this, be it remembered, refers to a very 

 restricted period in the history of our globe. It is that 

 space of time only, the events of which are most clearly 

 seen and understood by botanists. And it is so very 

 shoii, a space, compared with the spaces which come into 

 the estimates of geologists, that we can scarcely deem an 



