DISTRinUTIOX OF ANMMAI.S AND PLANTS IN KF.LSTEAD, ESSEX. 203 



the rank vegetation is cleared away year by year, the hedgerow will 

 be prolific of species and individuals. Any botanical collector can 

 verify this statement. In a new clearing certain species will some- 

 times become very prominent and give one the idea of great vigour 

 (Jack-by the-Hedge, Sisym/>riitm alliaria, is a good example). Yet on 

 reflection it must be seen that such plants are only tenants at will, 

 and if they had no assistance from the hand of man (in removing 

 obstructions) they must inevitably in a few generations become locally 

 extinct. Thus we see that in our restricted areas the struggle for 

 life by itself ultimately results in the local extinction of many forms 

 and in the preservation of a few. 



These notices of plants might be expanded to almost any extent. 

 I have quoted a well-known family, the Crowfoots, and, in opposition, 

 a family less well-known, the Orchids. We are in a better position 

 sometimes to deal historically with the less well-known. Notices of 

 their occurrence are in most lists definitely stated, whereas the 

 common forms are disposed of with a passing notice. This is un- 

 fortunate, for the mere collation of present with past lists would often 

 reveal incipient changes of distribution which could not be other 

 than instructive. It becomes therefore a question as to whether 

 a chronicle of abundant forms and the conditions under which they 

 maintain that abundancy is not a desideratum. 



To recapitulate briefly, we have found that the various species of 

 Freshwater and Land MoUusca are distributed unevenly in localities 

 separated by only a few miles and where direct communication is 

 often possible. That in time not long past their distribution was 

 greatly different from that at present obtaining. 



As regards the Fish, that in the river where communication is 

 still open certain species affect different parts of that river and that 

 the food supply appears to take no part in this separation. That, 

 withal, fish show much adaptability to circumstances, as seen in cases 

 of pond fish. These pond fish may be from their mode of occurrence 

 descendants of ancestors many generations removed. 



That among Reptiles Snakes are diminishing in a certain tract in 

 Essex from causes which cannot be certainly stated, and that the 

 extinction of Adders in the same tract may be due to the enclosure 

 and cultivation of the Commons. 



As regards the Plants, that they seem to show for any particular 

 locality a period of culmination and decay. That sporadic forms 

 seem to be connected with the preservation of germs which takes place 



