0 1 – 1 9 3 0 ) ▁ ▁Wel te v red en ▁ ▁In ▁ 1 9 0 1 ▁Back er ▁left ▁the ▁Netherlands ▁and ▁went ▁to ▁the ▁Dutch ▁East ▁Ind ies . ▁Between ▁ 1 9 0 1 ▁and ▁ 1 9 0 5 ▁he ▁was ▁employed ▁as ▁a ▁primary ▁school ▁teacher ▁at ▁a ▁private ▁board ing ▁school ▁in ▁Wel te v red en ▁( B at avia ), ▁( now ▁G amb ir , ▁the ▁centre ▁of ▁Jak arta ▁in ▁Java . ▁Im medi ately ▁he ▁started ▁to ▁collect ▁the ▁plants ▁around ▁him , ▁but ▁to ▁name ▁them ▁un re li able ▁or ▁incomplete ▁treat ises ▁had ▁been ▁written , ▁now ▁also ▁out dated ▁and ▁often ▁not ▁readily ▁available . ▁Thus , ▁he ▁decided ▁to ▁write ▁one ▁himself , ▁with ▁the ▁fl ora ▁of ▁his ▁immediate ▁surr ound ings ▁as ▁a ▁start , ▁and ▁this ▁marked ▁a ▁mil estone ▁in ▁his ▁life ▁and ▁for ▁M ales ian ▁bot any . ▁ ▁B uit enz org ▁ ▁He ▁came ▁into ▁contact ▁with ▁Mel ch ior ▁Tre ub ▁( 1 8 5 1 – 1 9 1 0 ), ▁the ▁Director ▁of ▁' s ▁Land s ▁Plant ent u in ▁in ▁B uit enz org ▁( now ▁the ▁Bog or ▁Botan ical ▁Gard ens ). ▁Through ▁Tre ub ’ s ▁med iation ▁Back er ▁was ▁given ▁an ▁appointment ▁as ▁Ass istant ▁at ▁the ▁Labor atory ▁with ▁as ▁instruction ▁to ▁write ▁a ▁critical ▁school ▁fl ora ▁for ▁Java ▁and ▁to ▁teach ▁at