150 years have passed since Darwin first published his famous book on evolution. The subject is as controversial today as it was when first introduced to the scientific world. Asa Gray was considered to be the leading botanist of the 19th century. Gray unified the taxonomic knowledge of the plants of North America. A book known simply as Gray's manual has been republished in many editions and is still a leading reference book in the field. Gray created a botany department at Harvard. These essays written by Gray cover a period of 16 years immediately after the publication of Darwin's Origin of Species by Means of Natural Selection. Gray's views make an interesting companion piece for anyone studying Darwin.