1. The relationship between seedling potential relative growth rate RGR and seed mass was investigated by growing in the glasshouse 26 species selected to form 13 phylogenetically independent contrasts (PICs). The two species in each PIC diverged at least 10-fold in seed mass and each PIC represented a phylogenetic branching independent of the other PICs in the study. 2. During the process of deployment following germination, seedlings undergo an initial dry mass decline before autographic growth overtakes respiration and mass begins to increase exponentially. This initial decline tended to be earlier and deeper in the smaller-seeded species of each PIC. Mass began to increase earlier in the smaller-seeded species in eight of the 13 PICs, there being no difference in the other five; the percentage mass decline from day 0 to day 2 was significantly greater in the smaller-seeded species in four of the 13 PICs, almost significantly greater in two further PICs and not different in seven PICs. 3. In all species exponential growth was under way by day 6 and continued through day 40. RGR was significantly different between the members of 12 of the 13 PICs. In 10 of these the larger-seeded member had slower RGR, vs the reverse relationship in two PICs, and there was also an overall negative correlation between seed mass and RGR considered across all 26 species. Thus the association reported in several previous studies between larger seed mass and slower potential seedling RGR occurs repeatedly within genera and families, as well as across older divergences between families and orders. 4. RGR differences within PICs were most often owing to differences in net assimilation rate (leaf mass basis) NARw, rather than to differences in allocation to leaf mass as a proportion of whole plant mass. 5. There were interesting unexplained patterns in the relationship of apical meristem volumes, measured at day 26, to seed mass. Root meristems were larger in the larger-seeded species in nine of 13 PICs (as perhaps might be expected, though there was little overall relationship between seed mass and meristem volume) but shoot meristems were larger in the smaller-seeded species in 11 of 13 PICs. Differences in meristem volume within PICs were considerable, often 10-fold.