His ambition at this period, which was also in accord with the dearest wishes of his parents, was to complete his college course and enter the ministry.

Illinois College not possessing a theological atmosphere after a year spent there he departed, and in 1857 began a course of study at Oberlin College, Ohio.
Among his studies there was botany, and in this class Powell at last discovered himself and his true vocation--the investigation of natural science.

He became an enthusiastic botanist and searched the woods and swamps around Oberlin with the same zeal and thoroughness which always characterised his work.

He made an almost complete herbarium of the flora of the county, organising the class into a club to assist in its collection.

In the summer of 1858, having returned to Wheaton, Illinois, where the family had settled in 1854, he joined the Illinois State Natural History Society, then engaged in conducting a natural history survey of the State through the voluntary labour of its members.