Stems of grass support much of the world's food supply during grain maturation. The purpose of this study was to determine the mechanical properties of stems and to determine if thick-walled, sclerenchyma cells are the main components that resist stem bending for 42 species of grass plants. During tests, stresses were imposed on grass stem segments to more than 90% of the maximum elastic load. Anatomical analyses were also performed to determine relationships between mechanical properties and geometric/anatomical characteristics of grass stems. Data show that more than 59% of all sclerenchyma cells in stems occur in the outer one-fifth radius of stems. Values of outer diameter, inner diameter, and stem density varied by factors of 10 or more, values of modulus of elasticity ranged from 0.1 to 32 GPa (a factor of more than 300 times) and values of maximum bending moment from 0.0005 to 2.0 N-m (a factor of 4000 times). Results of stress tests show that maximum bending moment was highly correlated with section modulus so that maximum bending stress values varied by only a factor of 8. Values of maximum bending stress varied from a low of 1.0E07 to a high of 8.0E07 Pa among the grass species tested with a mean and standard deviation of 3.3 and 2.3E07 Pa, respectively. Data of this study also showed that maximum bending moments of the 42 species were correlated well (y = 0.028x 0.0001, r2 = 0.64) with the areas of thick-walled sclerenchyma cells in stems. Taken together, these data show that maximum bending stress values of all 42 grass species were nearly identical and that sclerenchyma cells in stems provided the major support for stem integrity at the upper limit of imposed stem stresses. To our knowledge, this study is the first to compare the geometric, mechanical, and anatomical characteristics of over forty species of grasses to provide a unifying view of grass stem resistance to mechanical stresses.