136 THE TREES AND SHRUBS [LECT. 



Pliny, as indigenous to the countries in which they 

 are found. 



If the gaps which occur in the continuity of 

 these forests create a difficulty, if it be objected 

 that large intermediate spaces exist where such 

 trees are entirely wanting, it is much more easy to 

 conceive that they had died off in the latter locali- 

 ties, than that they had been planted in the coun- 

 tries where they are found through the instru- 

 mentality of man. 



Thus certain species of Oak seem to be under- 

 going diminution at the present time. Q. cerris, 

 spread over the whole of Asia Minor, is now 

 found in Europe only in a few isolated spots, as 

 in the Apennines, in Sicily, near Besangon, and 

 in the west of France along the Loire. 



The Pinus excelsa, so abundant in the Himalayas, 

 has been detected, as we have seen x , by Grisebach 

 on the mountains of Rumelia, but is not known 

 to occur in any intermediate position. These may 

 be regarded as oases in the midst of vast spaces 

 over which the species is unknown. The com- 

 mon Oak even seems to shew symptoms of wear- 

 ing out, not establishing itself spontaneously in 

 countries where it has been exterminated, and, where 

 it exists, suffering from the destruction of its forests 

 through the agency of man and beasts. On the 

 other hand the Beech appears to be extending itself 

 throughout Europe, owing partly to drainage, partly 

 to a fit soil being prepared for it by the detritus 

 * See p. 32. 



