182 
home, several fine herbaria of North American plants. In 
England, in 1814, he published his flora of North America, 
which was the second (and last successful) attempt to compre- 
hend in a single work descriptions of all known North American 
flowering plants. A few years later Pursh began the exploration 
of Canada, with a view to the preparation of a descriptive Cana- 
dian A but before this was accomplished he died, at Montreal. 
Thomas Nuttall was an Englishman who, when he came to 
America in 1808, at the age of twenty-two, had no knowledge 
of botany, and received his first lessons in that science from Pro- 
fessor B. S. Barton, to whom he had applied for information 
concerning an unfamiliar plant. Yet he became a great enthusiast 
in the pursuit of botanical ee and only ten years later 
he published his famous work on the genera of North American 
plants, which gave him a ee in the first rank of the botanists 
of his day. Meanwhile he had made excursions to various parts 
of the country east of the Mississippi, and one far up the 
Missouri, utilizing the inclement winter seasons for working up 
his collections at Philadelphia. Nuttall continued botanical work 
in this country until 1841, when he returned to England, where 
he spent his remaining years, with the exception of a brief visit 
to Philadelphia in the winter of 1847-4 
By the time Nuttall’s work on the genera of North American 
plants appeared, in 1818, there had sprung up two vigorous 
centers of botanical activity in this me one at Philadelphia, 
the other at New York. In disc g these, we shall find it 
convenient to take up the Philadelphia oe p of botanists first. 
This was doubtless directly influenced by the earlier work of the 
Bartrams and of Marshall in that vicinity. 
Henry Muhlenberg was a Lutheran clergyman, born in Penn- 
sylvania, but educated in Germany. He did not take up the 
study of botany until he was nearly thirty years old, about 1782 
or later. His home was at Lancaster from this time until his 
death in 1815, but he is mentioned here because his botanical 
associations were chiefly with the younger workers of Philadel- 
hia y his thorough work, his eh his collections, 
and his correspondence with European botanists, he did much to 
advance the knowledge of our flora. 
