Hesselmann[14], in his study of open woodlands in Sweden, has employed a method essentially similar to the preceding. Young plants of various species were transferred to pots in the field, where they were allowed to grow for several months before a series of weighings was made to determine the amount of transpiration. Since weighing is the measure used in each, both methods are equally accurate. The one has a certain advantage in that the pots are, perhaps, more easily handled, while the other has the advantage of maintaining the normal relation of soil and roots, a condition more or less impossible in a pot. In both instances the weighing should be done in the habitat, which was not the case in Hesselmann’s researches. The slight value of the potometer, which has had a vogue far beyond its merits, is indicated by the following table. These results were obtained from three plants of _Helianthus annuus_; III was left undisturbed in the pot where it had been growing, IV was placed in a potometer, after the root had been cut off, and V was an entire plant placed in a potometer. The amount of transpiration is indicated in grams per square decimeter of leaf surface. The plants were kept in diffuse light, except for a period of two hours (8:00 to 10:00 A.M.) on the last day, when they were in full sunshine at a temperature of 75° F. Plant IV wilted so promptly in the sunshine that it was found necessary to conclude the experiment in diffuse light. ═════╤═════╤═════╤═════╤═════╤═════╤═════╤═════╤═════╤═════╤═════╤═════ │ 8 │ 5 │ 8 │ 5 │ 8 │ 5 │ 8 │ 10 │ 5 │ 8 │Total │A.M. │P.M. │A.M. │P.M. │A.M. │P.M. │A.M. │A.M. │P.M. │A.M. │ ─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼───── III│ 2.9 │ 7.3 │ 2.4 │ 6.0 │ 1.7 │ 1.6 │ 2.0 │ 3.4 │ 2.0 │ 1.8 │31.1 IV│ 4.7 │ 7.2 │ 2.9 │ 2.3 │ 1.0 │ 0.6 │ 0.9 │ 0.5 │ 0.5 │ 0.4 │21.0 V│ 3.7 │ 5.3 │ 3.2 │ 4.8 │ 2.5 │ 1.6 │ 3.0 │ 2.6 │ 1.6 │ 2.6 │30.9 ─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴───── The cut plant, IV, lost more water the first day than either of the others, but the water loss soon decreased, and at the end of the period was almost nil. The total transpiration for III and V is much the same, but the range of variation for periods of 12 hours is from +2 to –1 gram. This experiment is taken as a fair warrant that the use of cut stems in potometers can not give accurate results. It is inconclusive, however, as to the merits of potometric values obtained by means of the entire plant, and further studies are now being made with reference to this point.