BOTANICAL SOCIETY OF LONDON. 
17 
for the sake of brevity, by the letters «, b, c. r l he subsoil in 
all is sandy or gravelly ; the ponds and the bog containing 
more or less of decayed vegetable matter, and many of 
the lanes immixing the gravel with clay or covering it 
with a rich mould. 
The dry gravelly fields, moreover, which bound the com- 
mon on the east, as well as the clayey or loamy lands, and 
the soft and often watery meadows lying further towards the 
east and the south, are particularly interesting to the agri- 
cultural Botanist. The letters cl and e might distinguish the 
herbage peculiar to sand or gravel, from that which delights 
in a stiff or moist clayey soil. 
The woods and groves, however, which surround the 
Common on every side, except the northern, are perhaps the 
most interesting parts of this vicinity ; the trees and shrubs 
shading the more feeble plants, partly on a dry surface, 
whether gravelly or clayey, partly amidst swampy bogs. 
These diversities might be marked by the letters f and g. 
But the wood that lies on the eastern side, contains the 
greatest and the most interesting variety of native produc- 
tions. 
The number of Genera of which I have seen specimens in 
the several stations described above, exceeds three hundred 
and forty, including ten Genera of ferns. Now, all the 
British Genera of the same kind, that is, of Phagnogamous 
plants and ferns, do not exceed four hundred and eighty. 
We have species, therefore, of nearly two thirds of this latter 
number, and on a superficies of less than two miles from its 
centre. The remaining genera belong, for the most part, to 
the sea-side, to chalky ground, or to high mountains. A few 
of the chalk-plants, indeed, are found in this locality, because 
a few spots are naturally somewhat marly, and the fields are 
often furnished with chalk or with lime, from Grays and 
Sifford, or from Purfleet. 
A deficiency will be observed in the number of Species, as 
compared with the number of Genera. This arises, in part, 
from the entire omission of the multitudinous species of 
Carex and of Salix, in part, from my having neglected to 
register a good many species that I had cursorily noticed, 
and in part, I fully believe, from a real deficiency of about 
one hundred species belonging to the genera comprised in 
this list. (A list of the genera and species here followed, of 
which the following is the summary : — ) 
c 
