Article (magazine)  (Jan 1955)  Page(s) 59.  
 
Alphabetical Check List of Tree Peony Names In  Public Collections And/or Available in Nurseries 1954-1955
Japanese, Purple, 'Negricans' (Jap. bef. 1864), [Gardens] Scott Foundation

Book  (1928)  Page(s) 261.  
 
Tree Peony Check List
*Negricans. Syns. Princess Amélie; Germania, Siebold. (Japan, 1864.) Haage & Schmidt 1864; E. H. Krelage 1867; Charles Van Geert 1874; A. Dessert 1899, 1905.

*Presumed to be in commerce, 1927.

Book  (1907)  Page(s) 157.  
 
1780. NEGRICANS; P. moutan.
(1) 1906, Dessert's Cat., p. 46.

Website/Catalog  (1903)  Page(s) 27.  
 
Pæonia Arborea (Tree Peonies)
The Tree Peony is really one of the finest plants available for the garden or the conservatory; it is quite hardy and does well under the simplest treatment. The smallest one will flourish in the most astonishing manner, bearing blossoms from 6 to 8 inches across, which will increase every year in beauty and size. In colors, the flowers range in great variety, from a white to a nearly reddish black. [...]
Price: Two-year old, named varieties, purchaser's selection, $1.25 each, $12.00 per dozen...
Nigricans. Reddish brown, nearly black in center, yellow stamen.