178 



Sub-formation of the Chalk 



la 



ca Orchis pyramidalis la 



ca 0. ustulata 1 



*0. Morio f 



0. maculata a 



ca Aceras anthropophora la 

 ea Ophrys apifera la 



oa C. f uciflora (arachnites) Tr 

 ca 0. sphegodes (aranifera) If 

 caHerminium Monorchis o 



* Habenaria conopsea 

 H. albida 



* H. viridis 

 ca Iris fcetidissima 



Luzula oarapestris 

 Carex flacca (glauca) 

 C. verna (prseoox) 

 C. humilis (olandestina) 

 Phleum pratense 

 Agrostis vulgaris 

 ca = calcicole 



caTrisetum flavesoens 

 caAvena pubescens 

 A. pratensis 

 Arrhenatherum elatius 

 Cynosurus criatatus 



Isd 



f 



ca Koeleria gracilis (cristata) f 



1 



Dactylis glomerata 

 * Briza media 

 ' Festuca rigida 

 F. elatior 

 caBromus ereotus 

 B. mollis 

 Brachypodium gracile 



(sylvaticum) 

 B. pinnatum 

 Lolium perenne 

 Ophioglossum vulgatum 

 Phegopteris Robertiana 

 (calcarea) 



specially abundant on chalk 



The following is a hypothetical scheme of the relation- 

 ships of the associations of the chalk sub-formation : — 



^Beechwood 



[with much yew] 



Ashwood 



%, 



Yew wood 



Chalk scrub + Yew groves 



i 



Chalk grassland -*-Chalk heath 

 t 



It will be useful to add some results of a detailed study of the com- 

 position of a small area of the chalk grassland association on Fleam 

 Dyke, Cambridgeshire'. 



Fleam Dyke is one of a series of very ancient military earthworks 

 occurring in south-east Cambridgeshire and extending in a south-easterly 

 direction from the Fenland to the chalk uplands, which are largely 



' The results of this study, which was carried out by the Marshall 

 Ward Society, of the University of Cambridge, were very kindly placed at 

 the Editor's disposal by Mr E. H. Compton, late Secretary of the Society. 



