The pollen grains of _Melilotus alba_ and of _M. officinalis_ are quite similar. Each grain contains three germ pores, and when viewed so that the pores are visible they present a slightly angled appearance. The average dimensions of the pollen of _Melilotus alba_ and of _M. officinalis_ are 26 by 32 microns and 24 by 30 microns, respectively, when measured in the positions shown in _b_ in Plate I, figure 6. The walls of the pollen grains have cutin deposited in them, as shown by their reactions with Sudan III, alkanin, safranin, and chloriodid of zinc. The contents of the pollen grains give a distinct reaction when tested for fat, and Millon's reagent shows that also some protein is present. Tests for sugars and starch showed that these substances are not present in perceptible quantities in mature pollen grains, although some starch is present in immature pollen. GERMINATION OF THE POLLEN. The germination of the pollen of _Melilotus alba_ permits considerable variation in moisture, as is illustrated in Table I. Table I.--_Germination of the pollen of Melilotus alba in water and in solutions of cane sugar of different strengths._ ---------------+--------+--------------------------------------- | | Cane sugar in solution (per cent). | Pure +----+----+----+----+----+----+----+---- Melilotus alba.| water. | 8 | 12 | 18 | 24 | 30 | 35 | 45 | 55 ---------------+--------+----+----+----+----+----+----+----+---- Germination | | | | | | | | | of pollen | 33 | 23 | 64 | 46 | 60 | 46 | 31 | 22 | 0 per cent | | | | | | | | | ---------------+--------+----+----+----+----+----+----+----+---- The results given in Table I represent the average of 12 tests. Some of the pollen grains burst in pure water and in the weak cane sugar solutions, the percentage of bursting being greatest in pure water and decreasing as the percentage of sugar in the solution was increased. There was considerable variation in the percentages of germination in both water and in the solutions of different strengths, and at times there was very little bursting which was not accompanied by a high percentage of germination. The pollen tubes grew as rapidly in water as in any of the sugar solutions, some reaching a length of 100 microns in six hours. As the pollen tubes made no more growth in the solutions of sugar than in water, it is evident that the sugar is not used as food, but helps in germination by reducing the rate at which water is absorbed.