126 THE JOURNAL OF BOTANY 



place where I have found the typical form. These and many 

 others are all good index species in working such a rock in our 

 Lincolnshire area. It must be remembered that index species 

 may be quite local. Wide field-work demonstrates that they 

 may be peculiar to a very limited area indeed as true index 

 species. This will be perfectly proved when the true ecological 

 method has been applied widely. For instance, Potentilla argentea 

 is the best index species for the Spilsby Sandstone in Lincoln- 

 shire. It is confined in this county solely to that bed ; but 

 beyond our area it is a mere sand index species. 



Not only do index species proclaim what exists now under 

 given circumstances, but they can be safely used to demonstrate 

 in limited areas what once existed, though the circumstances have 

 now completely changed. This is one of the great advantages of 

 intensive ecological study of limited areas when the results are 

 applied to solving the problems of county or vice-county floras. 



To give an instance of this, take the Pyrola. They are recog- 

 nised as woodland or woodland scrub species." In Lincolnshire 

 some most curious facts come out of a historical consideration of 

 the position in the past of our only species, P. minor. The great 

 block of parishes for which it is recorded lies on the eolian sands 

 at the foot of the escarpment of the wolds for a distance of eight 

 miles north and east of Market Easen. Now on these sands 

 Pimcs sylvestris grew as a self-sown species from prehistoric 

 times till about 1840, if not later. Beyond this area Pyrola is 

 found in a few isolated spots. These places are worth careful 

 study to see whether it is a good and safe index species of 

 ancient, but now departed, pinesques in this county. In 1840 it 

 was recorded, under the mistaken name of P. rotundifolia, for 

 Laughton Common.! This common was the centre of a vast 

 pinesque which flourished into historic times, and stretched north 

 to south for fifteen miles over the eolian sand dunes of the Trent 

 valley. I have personally seen tons of pine which have been dug 

 out of the peat in various parts of this old forest. One spot was 

 called Welfholme — a truly suggestive name for part of the forest 

 that once was there. P. media has been destroyed in this area 

 since 1840 by allowing rabbits to increase beyond all reason. | 



* The Marine Sand Dune variety arenaria of P. rotundifolia is no excep- 

 tion to the general rule ; where I have seen it growing in the valleys of the 

 Lancashire eolian hills, the ground was scrubby with Halix repens, &c. 



f There can be no question as to this, for the County Herbarium possesses 

 a specimen of P. minor from Nottingham named P. rotundifolia by the same 

 authority, the Rev. J. K. Miller, a very good botanist for his time (1787-1855). 



\ In the Journal of the Ecological Society, i. p. 273, some doubt is cast 

 on the point whether hungry rabbits will eat Senecio Jacohcea. I can only say 

 round the spot where P. minor formerly grew — for it is known exactly — 

 S. Jacobcea was badly eaten by them. The trees of a fagesque of forty years' 

 growth were badly barked, and many plants were locally exterminated along 

 with Pyrola. The most astonishing fact I discovered in this rabbit inquiry 

 \fa,sihe\ynyAnthriscusi'ulfia)is met and adapted itself to this rodent's appe- 

 tite. The plants were but four or five inches long, buried in moss completely 

 out of sight with the exception of their flowers and seeds. 



