Examination of chloroplast distribution in the parenchyma sheath cells of 59 species of panicoid grasses has revealed that the Euphanicoideae and the Chloridoideae differ for this character. In all 28 species of the Eupanicoideae the chloroplasts, when devoid of starch, are grouped in the outer (centrifugal) region of the parenchyma sheath cells. Among the Chloridoideae, except the tribe Sporoboleae, the chloroplasts are grouped in the inner (centripetal) region of the cells. Both conditions in about equal numbers of species were found in the Sporoboleae. The distribution of chlroplasts is probably associated with the different physiological activities of chloroplasts in these two subgroups of the Panicoideae. Among the various major subgroups of the grass family there are many differences of anatomy, physiology, cytology, ecology, histology, and embryology (Stebbins, 1956; Brown, 1958). Recently Stebbins (1959) has compiled a list of 36 characters that can be used to separate grass tribes and recognize affinities among genera. The two major subgroups of the subfamily Panicoideae, the Eupanicoideae and Choridoideae, differ with respect to leaf histology (Prat, 1936); presence or absence of the epiblast (Reeder, 1957); and in leaf anatomy (Brown, 1958). Recently a new diffierence was detected between these two groups. While examining microscope slides used in the preparation of a paper to be presented before the 9th International Botanical Congress (Brown, 1959) and which had served as the basis for a previous paper (Brown, 1958) it was noticed that in the parenchyma sheath cells of the Panicoideae the chloroplasts, when not full of starch grains, occupied positions either close to the inner (centripetal) wall or near the outer (centrifugal) wall. It seemed that the outer position occurred in eupanicoid species whereas the inner position was characteristic of the Chloridoideae (fig. 1 and 2). All available slides of leaf cross sections of species in these groups were examined and information on chloroplast location recorded (table 1). Data were collected from 59 species, of 44 genera, of 8 tribes. In all 28 species of Eupanicoideae the chloroplasts were grouped in the outer region of the parenchyma sheath cells. Among the Chlori-