Book  (1927)  Page(s) 22.  
 
In Pasadena [California] are the Rare Plant Gardens of D.W. Coolidge, which are a Mecca for whoever is in search of the latest plant novelties. Many Californians believe that Coolidge's understock variety, which he calls "I.X.L." will supplant all other stocks, by reason of its vigor and the fact that it is thornless...

Book  (1926)  Page(s) 184.  
 
I.X.L. Hybrid Multiflora (D.W. Coolidge, 1925). 'Tausendschön' x 'Veilchenblau'. Said to be a composite of both parents but not so dark as 'Veilchenblau'... Reported to be chiefly valuable as an understock being more vigorous than any stock now used, throwing up straight canes an inch in diameter without thorns.