Asa Gray, Albumen print, ca. 1863-1864.

Asa Gray survived Darwin by almost six years. Before he lapsed into speechlessness—a condition that continued for a month—the last work he finished was a review of The Life and Letters of Charles Darwin. In 1882, he had ended his obituary for his good friend Darwin with the following prophetic sentences: “How far and how long the Darwinian theory will hold good, the future will determine. But in its essential elements ... it is an advance from which it is evidently impossible to recede.” 

The revenue stamp verso dates the portrait between 1 September 1864, when the U. S. Federal Government, in order to help finance the Civil War approved a 3 cents tax on all photographs sold in the United States, and 1 August 1866, when, following a repeal in Congress, the tax was no longer required. A 3 cent stamp would have meant that this carte-de-visite cost over 25 cents.