Magazine  (28 Jul 1937)  Page(s) 56.  
 
Other beautiful varieties not yet available here [in the U.S.] are W. E. Gladstone (lilac), Otto Froebel (gray with a lovely flush), Perle d'Azur (light blue), blooming on new wood, and La Lorraine (pink suffused with lavender) and Edouard Desfossé (violet with deeper bars), blooming on old wood.

Website/Catalog  (1912)  Page(s) 78.  
 
Summer and Autumn Clematis.
In bloom from July to October.
These flower upon the wood of the current year's growth, and should therefore be pruned to five or six eyes.  
Otto Froebel, beautiful greyish white...  1s. 6d.

Website/Catalog  (1907)  Page(s) 66.  
 
Clematis in pots to plant out in spring and summer.
General Collection.
73 Otto Frœbel (lanuginosa), greyish white.

Book  (1906)  Page(s) 53.  
 
Principal garden varieties of Clematis:
Lanuginosa type. (July to October.)
Otto Froebel... Greyish-white, large.

Magazine  (1900)  Page(s) 316.  
 
from "Hybrid Clematis" By Mr. A. G. Jackman, F.R.H.S.
Among the foremost hybridisers of the Clematis must also be mentioned Monsieur Lemoine of Nancy, who has raised several good varieties of the patens, lanuginosa and viticella types of recent years... C. Otto Froebel [...] of the second type...

Book  (1898)  Page(s) 3.  
 
Les premières obtentions de M. Lemoine, de Nancy, furent: les Clematis lanuginosa candida, C. lanuginosa nivea, C. Otto Frœbel.

Book  (1898)  Page(s) 64.  
 
Variétés Horticoles
1er Groupe.—PATENS
Section II. — Lanuginosa.
Otto Frœbel (Lemoine). Très belle et large fleur blanc rosé.

Magazine  (28 Oct 1882)  Page(s) 414.  
 
The Clematis in the Midlands.
...The sorts I have most successfully grown are the following, and the mode of cultivation that recommended by Mr. Jackman.  Lanuginosa type: Gem, lanuginosa, lanuginosa candida, Otto Frœbel, Princess of Wales, purpurea elegans, Gloire de St. Julienne.

Magazine  (1880)  Page(s) 194.  
 
Lanuginosa Otto Frœbel. Fleurs lilas clair, atteignant 20 à 22 cent. de diamètre, variété très remarquable, fleurit depuis août jusqu'à novembre.

Magazine  (1877)  Page(s) 261, 270.  
 
p. 261: Cl. lan. Otto Froebel. — Hort. franç.. 1869, 347.

p. 270: Clematis Otto Frœbel (Lemoine), s. des lanuginosa: lilas rosé.