iXTRODUCTiox Hii 



stream, which soon enters Surrey, and after a course of a few miles 

 falls into the Thames below Chertsey. 



THE BOTANICAL DISTRICTS. 



From the manner in which the Thames serves as a boundary to 

 Berkshire on the northern and eastern side, considerable difficulty 

 has been met with in dividing the county into botanical districts, 

 which shall be representative of the streams by which they are 

 drained. Various plans have been considered, and much may be said 

 for and against those which have been examined and rejected. The 

 following arrangement, which has been finally chosen, is by no 

 means free from objections, but it appears on the whole preferable 

 to any, except one in which a very large number of districts would 

 have to be employed, and such a plan it did not seem desirable to 

 adopt in a county of so small an area as Berkshire. Several friends 

 have urged the desirableness of making the districts purely artificial, 

 a plan followed by Mr. Britten in his Contributions, but almost all our 

 recent Floras have made the river-basins the basis for the division of 

 the areas they treat of into districts. A second series of advisers 

 strongly recommended the adoption of districts based on the various 

 geological formations, and this plan commended itself to the author 

 until he attempted to put it into practice. The objections to it need 

 not be given at length, but the influence of the great extent of drift 

 deposits was one of the chief reasons which led him to give up the 

 idea of basing the districts upon the geological strata, and to adopt the 

 system of river drainage as in the Floras of the neighbouring counties, 

 Hampshire, Wiltshire, and Oxfordshire ; and as from the two former 

 counties Berkshire receives the Loddon and the Kennet respectively, 

 by adopting botanical districts based upon the river draina:;e, Berk- 

 shire is brought into harmony with its neighbours, and those botanists 

 who are interested in the plant distribution through the smaller river 

 districts of England, may have less trouble in tracing the constituents 

 of each river-flora than would be the case if an artificial or geological 

 basis of division had been followed. 



The Botanical districts or divisions of Berkshire that have been 

 adopted are five in number, namely : — 



1. The Isis or Upper Thames, which corresponds to the district 

 ' Thames 3 ' of Preston's Wiltshire Flora, and to the district * 5. Isis or 

 Upper Thames,' of my Floi-a of Oxfordshire. 



2. The Ock, an entirely Berkshire stream, which has its counter- 

 part in the district ' 6. The Thame,' in my Flora of Oxfordshire. 



3. The Pang or Mid Thames, which bears considerable resemblance 

 to the district ' 7. The Thames,' of my Flora of Oxfordshire. 



4. The Kennet and Lambourn, which is the Berkshire continua- 



