1 90 Flowers and their Pedigrees. 



but of late years it has grown rarer and rarer with 

 each succeeding summer, until it is now probably 

 quite extinct. It is the natural tendency of all such 

 small isolated colonies, whether of plants or animals, 

 to die slowly out ; for they cannot cross freely with 

 any of their own kind outside the narrow limits 

 of their own restricted community ; and by con- 

 stantly breeding- ui and in with ono another they 

 at last acquire such weak and feeble constitu- 

 tions that they finally dwindle away imperceptibly 

 for want of a healthy infusion of fresh external 

 blood. 



If I mention a few other like cases (as well as I 

 can remember them on the spur of the moment, for I 

 cannot pretend to give a complete ex-cathedra list 

 here on the slopes of Mynydd Mawr) it will help to 

 elucidate the origin and nature of this little colony of 

 mountain tulips. There is a lovely orchid, the lady's 

 slipper, common in Siberia and Russia, almost up to 

 the Arctic Circle, but now found with us only in one 

 Yorkshire station, where, like the Perthshire heath, it 

 is rapidly verging to complci;- local extinction. Again, 

 among one family alone, the tufted saxifrage has now 

 been driven to the summits of Ben Avers and Ben 

 Nevis ; the drooping saxifrage is extinct everywhere 

 in Britain save on the cloudy top of Ben Lawers ; the 



