INDEX SPECIES IN A FLORA 125 



was looked on as astonishing by other workers because they had 

 never given their minds to true observation." 



Surely true ecology (useful but hateful word !) is the art of 

 observing the sequences in nature which follow from changed 

 circumstances. Master the natural surroundings of the plants 

 under all conditions, then the slightest change of circumstance 

 even when invisible, as in the case given, will be clearly demon- 

 strated to the mind. Other instances of invisible influences are 

 easily given. The Chalky Boulder Clay lying in Lincolnshire 

 west of its mother rock, the high Chalk of the Wolds, is not a 

 fairly uniform bed of clay like the Oxford and Kimmeridge Clays. 

 It is made up of layers growing more and more chalky till the 

 basement layer is reached. The lowest zone may contain as much 

 as 90 per cent, of carbonate of lime ; or, in other words, practi- 

 cally be chalk moved to another situation. In working a Chalky 

 Boulder Clay area of any considerable size, lying near its mother 

 rock, it will be observed that where the bed feathers out to a thin 

 edge I on the rock below, or where the streams which drain it 

 have cut shallow valleys through its upper and more clayey layers 

 into its lower and more chalky depths, the flora at once shows 

 a change of species : in pasture by the appearance of Plantago 

 media, in hedges of Sison Amomum, and generally by the coming 

 in of Senecio erncifolms, and such species in ditches as Ranunculus 

 auricomus, var. depauperata, or var. apetala. I have never found 

 the typical plant under such circumstances. 



The Lower Lias Clays and Limestones give a similar set of 

 varying circumstances, but caused in another way, and generally 

 more visible. These beds were laid down in a fairly shallow sea- 

 bottom not far from land, and consist of thick masses of stiff blue 

 clay interstratified with beds of good building limestone, which, 

 being more resisting to denudation than the clay, frequently make 

 low escarpments. The flora at once indicates the change from 

 clay to stone, though the outcropping zones of limestone are 

 sometimes practically invisible and not more than a few yards 

 across. Campanula glomerata appears on the narrowest zones, 

 and C. Trachelium and C. latifoUa along with it on the wider ; 

 and B. auricomus is found also in its most perfect state — the only 



* I noted at the time, for I was specially collecting insect visitors that day, 

 that Buinbus agrorum — the only humble-bee that I have ever personally recorded 

 as visiting Stachys j^alustris for honey, though Mr. G. ¥. Scott-Elliot has 

 recorded three others — only flew as far as this spot on the dyke. It sucked 

 honey, and then circled round and round, and finally returned by the way it 

 had come, along the upland part of the dyke, quite omitting the marsh stretch 

 below. I do not mean to imply by this that B. agronim is not a marshland 

 species. It is common enough here on our peat carrs, often taken on Lythrmn ; 

 in fact, the only species of Bombus I have ever taken personally on it, though 

 Mr. Scott-EUict records two others. I simply wish it to be understood that the 

 bees observed that day did not mix the honey taken from the upland flora at 

 this junction spot with that from the true marsh species. This fact is, I take 

 it, worth record. 



t This feather edge is beloved of certain plants, and also varieties of Helix 

 virgata, which are not found on the more clayey masses above. 



