Magazine  (1966)  Page(s) No. 164, p. 275.  
 
Clematis (hybrids)...
From France. Plants presented by Andra Girault, Horticulteur-Pepinieriste, Orleans (Loiret). Received Nov. 18, 1959.
...261350. 'Gem'.

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.  
Gem, deep lavender blue; very fine..  1s. 6d

Book  (1906)  Page(s) 52.  
 
Principal garden varieties of Clematis:
Lanuginosa type. (July to October.)
Gem... Deep lavender-blue.

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  (1877)  Page(s) 268.  
 
Clematis Gem (Baker); bleu.