120 The Flora of Wiitshire. 
net and the Bristol Avon. This is about 57 miles long, it com- 
mences at the head of the river Kennet at Newbury in Berkshire, 
and terminates in the river Avon at Bath. About 41 miles of its 
course is in Wiltshire, which it enters near Hungerford. It passes 
Great Bedwyn, Devizes, and Trowbridge, and quits the county 4 
miles from Bradford, at the Dundas Aqueduct. 
3rd. The Wilts and Berks Canal, which connects the Thames near 
Abingdon, with the Kennet and Avon Canal, at Semington between 
Devizes and Bradford. 
Boranicat Drvisions. 
In arranging a county into divisions and districts for purposes of 
Natural History, no doubt the principle of adhering to watersheds 
as boundary lines, so rigidly carried out in the excellent “Flora of 
Hertfordshire,” is the sound one, viz,, that each tributary, even the 
smallest streamlet, shall be taken with the main stream into which 
it runs. But practically this becomes exceedingly inconvenient, 
the lines of demarcation being unmarked on maps, and difficult to 
find on the real ground. 
A more convenient course and one as applicable to the actual 
distribution of plants is to seize upon some good visible boundaries, 
however artificial, which approximate to the watershed lines, al- 
though not very exactly. Of this kind are canals, large streams, 
railroads, and highroads, being evident on the ground, and usually 
traced on maps. These will, therefore, be taken as being best 
adapted for dividing the county into districts for botanical study ; 
for all Floras should be sectional, they should be not only a small 
whole in their local uses and purposes, but also a part of something 
larger and wider, and such a part as may be united, uniformly 
and congruously with the other parts, into the one greater whole. 
The Kennet and Avon Canal is, therefore, fixed on as one very 
visible boundary, right across the county, and tolerably well cor- 
responding with its most important watershed, that namely, which 
cuts off the southern from the northern portion of the county.! The 
' See map of ‘The Botanico-Geographical Districts of the County,’ accom- 
panying this paper. 
