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fessor B. S. Barton, to whom he had applied for information con- 

 cerning an unfamih'ar plant. Yet he became a great enthusiast 

 in the pursuit of botanical knowledge, and only ten years later 

 he published his famous work on the genera of North American 

 plants, which gave him a place 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 Mis- 

 souri, 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 1847-48. 



By the time Nuttall's work on the genera of North American 

 plants appeared, in 18 18, there had sprung up two vigorous 

 centers of botanical activity in this country, one at Philadelphia, 

 the other at New York. In discussing these, we shall find it 

 convenient to take up the Philadelphia group 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 18 15, but he is mentioned here because his botanical 

 associations were chiefly with the younger workers of Philadel- 

 phia. By his thorough work, his publications, his collections, 

 and his correspondence with European botanists, he did much to 

 advance the knowledge of our flora. 



Dr. Benjamin Smith Barton, a native of Pennsylvania, who had 

 received his medical education at Edinburgh and Gottingen, be- 

 came a professor in the University of Pennsylvania in 1790, at 

 the early age of twenty-four, and continued to occupy this chair 

 until his death twenty-five years later. His position gave him 

 much prestige, and his contributions to the advance of American 

 botany are to be measured less by his published work than by 

 the influence of his botanical lectures, and the sympathy and 

 financial support given by him to other students, such as Pursh 



