PLANT PHYSIOLOGY periments in which we have confirmed the observation by Galston and Baker (2) that elongation in the dark of green pea stem segments is much more dependent upon sucrose than is the elongation of etiolated stem segments. Furthermore, since we have detected no promotion by cobalt of the growth of the green segments, the condition affected by cobalt apparently is not limiting to elongation. In one experiment, the elongation of such stem segments (originally 5.3 nun long) was L52 mm on 10 mg/l IAA, and 4.02 mm on IAA plus 2% sucrose. The elongation on either solution was not increased by inclusion of CoC12 in the concentration range from 4 to 20 x 10-5 M. SUMMARYSucrose in some experiments slightly promoted and in others slightly inhibited the elongation of sub-apical segments from etiolated pea stems. The sugar, however, markedly increased the fresh weights of the segments. Cobaltous salts, when added to test solutions containing only indole-3-acetic acid (IAA), slightly promoted elongation. When sugar and cobalt were added together to the IAA solution, great increases of elongation occurred. The evidence reveals a distinction between the roles of water uptake and cell wall increase in the enlargement of plant cells.It is suggested that sucrose increases cell volume and that cobalt promotes the ability of the cell walls to increase in surface area.

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