The temperature field of axisymmetric laminar plumes generated in water from a small heat source located in a large horizontal plane was measured interferometrically for heat injection rates of 1.5 and 0.72 cal/sec at heights of up to 19 cm above the source. For a height of 19 cm and heat injection rate of 1.5 cal/sec, steady state was reached within 5 sec of the passage of the starting cap; an axial temperature of 3.1° C above ambient was measured, and the diameter at half that temperature was 4 mm. The experimental results were compared with previous analytic solutions for plumes generated from ideal isolated point sources. Good agreement was obtained if the concept of an apparent source is utilized.