216 THE NATURAL HTSTORT REVIEW. 



witliin the short period of direct and positive botanical history. 

 Three centuries are as nothing in the long life of a species which 

 usually preserves its powers of reproduction to the last, so as under 

 favourable circumstances rapidly to regain any ground it may have 

 lost. But whether it may be that in some instances these powers of 

 reproduction do become weakened by time, or that new enemies, 

 animated or physical, arise, or the old ones increase in number or 

 power, a period arrives when the balance is destroyed, the area of a 

 plant is gradually restricted, its numbers diminish ; as it becomes 

 rare its position is more and more difficult ; it is restricted at last to 

 a single station, where a final blow extinguishes it. 



Three species, none of them as yet showing any approach to a 

 general extinction, are nevertheless supposed to have finally with- 

 drawn from Britain, or very nearly so, within the last hundred years, 

 without their destruction being traceable in any considerable degree 

 to human agency. Senecio paludosus is believed to have quite dis- 

 appeared from the fens of East England, and the same has been 

 recently said of Sonchus palustris. Menziesia coendea, from the 

 Scotch Highlands, was also confidently reported as extinct, but Dr. 

 Balfour, as we learn, exhibited at the last meeting of the British 

 Association at Bath, recently gathered specimens. That this species 

 has great inherent specific vitality is shown by its endurance in an 

 isolated, unfrequented spot in the heart of the Pyrenees, and that 

 the Senecio and the Sonchus have considerable powers of reproduc- 

 tion is equally proved by their occasional abundance in some parts 

 of the Netherlands and adjoining countries, but neither of these qua- 

 lities is sufficient without the other. The Menziesia appears not to 

 regain the footing it has once lost, whilst the two others have equal 

 difficulty in retaining the territory they have recovered. The above 

 mentioned Arum arisarum of the South belongs probably to the first 

 of these categories. 



We have also a few species, as, for example, Lolelia urens and 

 Simethis bicolor, which, like Glohularia, Alyssum and Anthyllis harba- 

 Jovis at Montpellier, although still tolerably abundant in restricted 

 localities, may be gradually disappearing from among us by 

 the same slow course of nature — that is, by a combination of 

 causes weighing down the balance against them. But it may take 

 many centuries yet to extinguish them altogether. The Simethis is, 

 we believe, a long-lived plant, whose grass-like leaves are lost for a 

 great portion of the year, and it may exist in small numbers, un- 



