UPON THE BRITISH FLORA. 13 



their migration, the temperature of these islands was much higher 

 than it is at present. Physical changes, climatal alternations, 

 and waves of migrations, make the exact successional order of 

 the deposits uncertain ; but a definite historical record is being 

 gradually built up by a comparison and correlation of the 

 numerous records. The work has been greatly facilitated by a 

 detailed examination of extensive areas. There are some British 

 botanists who ignore the essential differences between a varietal 

 form due to local conditions, and a true sub-species (for many of 

 our so-named sub-species have no more claim to separation than 

 luxuriant garden specimens). For instance the interminable 

 forms of the Water-crowfoot and the Lesser Spearwort growing in a 

 well-manured horse-pond have no claim to be considered to be 

 sub-species unless found under more natural conditions. Mr. 

 Clement Reid and Mr. Edmund Baker examined Saxifraga 

 umbrosa at its well-known habitat, Dingle Promontory with its 

 allied forms, each occupying well-defined areas, showing well- 

 marked off-type characters, and in proportion as more and 

 more of the patches were examined, these distinctions melted 

 away, so that finally nearly a complete series of intermediates 

 was obtained, the extreme at one end appearing to connect it 

 with Saxifraga Geum, growing in the same area. They were 

 evidently not hybrids. Botanical works are full of anomalies of 

 this sort, often due to a desire to announce the discovery of 

 a new form. No family has suffered more in this direction 

 than the Rubi, which happens to possess a remarkable power of 

 variation. 



The Lusitanian forms which originated in the Spanish 

 Peninsula were able to make their way to North Africa, which 

 had then a land communication with Spain ; this may be inferred 

 by so many of the groups growing in Morocco, and reaching 

 from the coast to the Atlas Mountains, whereas none of the 

 characteristic Lusitanian plants are found in Tunis, where the 

 Oriental section of the British Flora is represented by many 

 species. The two plants of the Lusitanian group especially cited 

 by Forbes are Arbutus Unedo and Euphorbia hyberna. It has 



