OEIGIN OP LOCAL FLOEAS. 
39 
{Ammopliila arundinacea) , covering tlie dunes or hills of blown 
sand on the American shores of Atlantic City_, New Jersey_, I 
cannot help feeling convinced that these plants are the natural 
growths of the country. And not only the marine_, but the fresh- 
water plants of Pennsylvania are in numerous instances the 
same as those found in the British Isles. Of twelve species of 
pond weed (Fotamogeton), eight are indigenous to Britain. The 
genera of the order Naiadacece are all British plants. Every 
stagnant pool is covered with duckmeat [Lemna minor), and 
the water star- grass [Gallitriche verna) floats there^ as here^ its 
beautiful green stars on the surface of running streams. In 
fact_, the lower we descend in nature^ the more the flora of 
both countries approximates. The mosses and lichens of 
Pennsylvania^ with but few exceptions^ are the same as those 
of Great Britain. 
How are these facts to be accounted for ? Here we have 
the same plants growing in similar localities thousands of miles 
apart from each other. If I may venture an opinion as to the 
causes which have led to this similarity between the vegetation 
of Pennsylvania and that of the British Isles^ I would say it 
is because the conditions that prevail on the sea-coasts^ and in 
the fresh-water marshes and streams of both countries, are 
very similar. The same ocean washes their shores, and the 
difference of latitude is only about 11^° or 10°. The latitude 
of Philadelphia is 39° 57' N., New York 40° 43' N., and that 
of London 51° 31' N. It is true that the summers of the State 
of Pennsylvania are much hotter, and the winters much colder, 
than those of England. Yet, in both countries on the sea 
coast, the great body of salt water tends to produce there a 
greater uniformity of temperature through the year than pre- 
vails inland. Nevertheless, it is hard to believe that mosses, 
lichens, and ferns, originated without spores, or that sundews, 
sea-plantains, glassworts, and sand-reeds, were created in 
these localities without seed. There is nothing in nature to 
justify such an hypothesis. It is undeniable also from these 
ptyto -geographical facts, that where similar conditions prevail, 
the same plants are found. But if the conditions have sur- 
vived the geological revolutions which have dissevered the 
species, this accounts for their existence and disjunction, with- 
out resorting to an assumption (which the progress of science is 
rendering every day more improbable) that plants were created 
directly out of inorganic matter, independently of spores and 
seeds. The same species would still survive, though moun- 
tains should rise and oceans roll between them, and continue 
unchanged through all the mutations of physical nature and 
the lapse of ages. 
