Abstract(1) The ratio of14CO2uptake of fully expanded capsules to that of corresponding gametophytes in the species studied was about 1 : 15 inMnium hornum,1 : 35 inPleurldium acuminatumand around 1 : 1 inFunaria hygrometriea.(2) Translocation of photosynthate from gametophyte to sporophyte took place within 1 to 4 days of exposure to14CO2; in expanded capsules the final activity was at least equal to that remaining in the gametophyte.(3) InM hornumthere was no evidence of reverse translocation from sporophyte to gametophyte.(4) Translocation from gametophyte continued at a high level throughout the expansion and differentiation of the capsule inM. hornum.The activity reaching the sporophyte was approximately proportional to its fresh weight.(5) Bothin situphotosynthesis and translocation to the capsule ofF. hygrometricarose to a maximum during the latter part of capsule expansion and ensuing differentiation, subsequently declining as the green tissues of the capsule senesced.(6) Fully expanded (but premeiotic) capsules ofM. hornumcontributed approximately 20% of the assiinilate necessary for their growth. The corresponding figure forP. acuminatumwas about 10%, and forF. hygrometricaabout 50%.