A temporary immersion bioreactor (10) for in vitro production of differentiated plant biomass including a growth chamber (12) having one or more transparent side walls (14) and a mesh bottom (16), the mesh bottom (16) defining a plurality of pores (18) to receive plant material. The bioreactor (10) includes a flexible bag (20) formed from a transparent material, the flexible bag (20) having a sealable opening and being dimensioned to receive the growth chamber (12) together with a liquid medium (22). The bioreactor (10) also includes an outer chamber (24) having one or more transparent side walls (26). the outer chamber (24) is formed to correspond in shape to the growth chamber (12) and dimensioned to receive the growth chamber (12) within the flexible bag (20) so that the mesh bottom (16) of the growth chamber (12) faces a bottom (28) of the outer chamber (24) that in use is intended to rest on a support surface. Movement of the growth chamber (12) within the outer chamber (24) is restrained to movement alo
