The growth and development of the pods and seeds of Senna macranthera (Colladon) var. nervosa (Vogel) Irwin & Barneby were morphologically and anatomically studied, and the variation in soluble carbohydrates and galactomannan deposition analyzed. Based on the morpho-anatomical changes, the developmental process was subdivided into 10 stages from anthesis until maturation. This allowed the sampling of fruits of similar development in each phase, in spite of the various stages attained by different fruits at every period of time. Aqueous ethanol-soluble carbohydrates increased gradually in the pods and decreased in the seeds during the process, the opposite occurring with the hot water-soluble ones. A massive deposition of galactomannan in seeds was observed in the phases immediately prior to seed and pod dessication. The mannose:galactose ratio of the seed and pod galactomannans varied from 1:3 in the beginning of deposition to 3.5:1 in the mature dry organs. It is shown for the first time that polysaccharides of the same composition and mannose:galactose proportions of seed galactomannan were detected in the pod (up to nearly 10% of dry mass) prior to its increase in the seeds. Considering the known functions of galactomannans, we suggest that pod galactomannan of S. macranthera var. nervosa could provide protection and maintenance of adequate humid environment for the development of seeds.