▁Cambridge ▁fac ulty ▁of ▁history ▁Category : 2 0 th - century ▁British ▁histor ians ▁Category : 2 1 st - century ▁British ▁histor ians <0x0A> </s> ▁The ▁Ar bor et um ▁Kal m th out ▁is ▁a ▁botan ical ▁garden ▁in ▁Kal m th out , ▁Belg ium . ▁It ▁was ▁started ▁as ▁a ▁tree ▁plant ation ▁by ▁Charles ▁Van ▁Ge ert ▁in ▁ 1 8 5 6 . ▁Van ▁Ge ert ▁developed ▁a ▁collection ▁of ▁rare ▁plants ▁and ▁trees ▁before ▁s elling ▁the ▁property ▁after ▁ 4 0 ▁years ▁to ▁Antoine ▁K ort . ▁K ort ▁added ▁an ▁extensive ▁collection ▁of ▁Ham am el is ▁to ▁the ▁nur ser y , ▁but ▁was ▁forced ▁to ▁close ▁his ▁business ▁due ▁to ▁the ▁Great ▁De pression ▁of ▁the ▁ 1 9 3 0 s . ▁In ▁ 1 9 5 2 , ▁the ▁property ▁was ▁purchased ▁by ▁the ▁brothers ▁Georges ▁and ▁Robert ▁de ▁Bel der , ▁to ▁save ▁it ▁from ▁being ▁destroyed ▁by ▁a ▁housing ▁development . ▁At ▁the ▁site , ▁the ▁year ▁that ▁they ▁purchased ▁the ▁property , ▁the ▁de ▁Bel der ▁brothers ▁founded ▁the ▁International ▁D end ro log y ▁Society ▁( ID S ) ▁to ▁promote ▁pres ervation ▁and ▁conservation ▁of ▁rare ▁or ▁end anger ed ▁wo ody ▁plants . ▁Robert ▁de ▁Bel der ▁and ▁his ▁wife , ▁J el ena ▁de ▁Bel der - K ova č ič ▁worked ▁together ▁to ▁build ▁an ▁intern ation ally ▁known ▁ar bor et um , ▁where ▁plant ▁enthus iast s ▁could ▁study