Six taxa of floating-leaved and submerged-leaved water plants were planted in artificial ponds in Kampala, Uganda. The substratum was divided into nutrient-rich mud and nutrient-poor sand sections, but the waters were homogeneously mesotrophic. The plants were harvested from 8 to 15 weeks after planting. Growth rates, in mg dry weight plant1 day1, were calculated for roots and shoots. The growth rate of the totally submerged rootless species, Ceratophyllum demersum, was least affected by substratum whilst the floating-leaved, rooted species, Potamogeton thunbergii, showed a four-fold increase on mud. This was reflected in ratios of growth rates of root/shoot of the rooted taxa. The ratios were higher when plants were grown in washed sand, but P. schweinfurthii, a submerged species, showed only a small increase whereas P. thunbergii had a nine-fold greater root/shoot growth rate ratio on sand than on mud. It is concluded that nutrients may enter through roots and shoots, but in some circumstances entry may be through roots or shoots alone.