The Dorchester Blackberry was first brought to the notice at the Massachusetts Horticultural Society in 1841 by Eliphalet Thayer of Dorchester. The entry in the Cyclopedia of Hardy Fruits says that the fruit is excellent. The plant was described as vigorous, upright, stocky, rather tender to cold, moderately productive, with numerous strong prickles. Fruit early, of medium size, glossy black, elongated; flesh rather soft, sweet, rich; quality good.
Eliphalet Thayer, 1789-1867, was a farmer in Dorchester.
In 1857 The Magazine of Horticulture stated that the Dorchester blackberry was underrated. “The fruit is considerably larger than the Lawton; it is a much firmer berry; holds its brilliant glossy color after gathering; bears carriage well; and is sweet and excellent even before it is fully ripe. … The Dorchester blackberry was for a long time called the Improved High Bush, and in consequence has been supposed, by a majority of cultivators, to be nothing but the wild blackberry improved by culture. This, however is not so; it is a seedling which originated in Dorchester, and was introduced to notice upwards of ten years ago, by the late Samuel Downer of that place.”
Thayer was probably the hybridizer who first grew the Dorchester blackberry, but Downer later grew the plant on his estate and publicized it. Downer was manufacturer of candles and of lard, whale and sperm oil for lubricating purposes. After the discovery of what became Kerosene, Downer began manufacturing illumination oil from coal. His company was the first large-scale producer. His success allowed Downer to be a gentleman farmer.
Sources:
Hedrick, U. P. Cyclopedia of Hardy Fruits. (Bedford, MA, 1922), 286.
The Magazine of Horticulture, Botany, and All Useful Discoveries and Improvements in Rural Affairs. v. 23 (Boston, 1857), 401-403.