This is an experimental study of the discharge of seeds in a silo in a mass flow regime. It demonstrates how the flow parameters involved in Beverloo's equation (C and k) can be correlated with some of the shape parameters belonging to the seed grains. Results show that the concept of empty annulus introduced through the parameter k is dependent on the size and on the specific surface area. Besides, the circularity of the grains, alone, is not enough to predict the value of kin a grain discharging process. (C)2017 Elsevier B.V. All rights reserved.