Development of the Ovules and Pollen in Sweet Clover. Fig. 1.--Section through the nucellus of an ovule of _Melilotus alba_, showing two megaspore mother cells. × 360. Fig. 2.--Median section through an ovule of _Melilotus alba_, showing the two cells resulting from the first division of the megaspore mother cell, and the relative development of the different parts of the ovule. × 300. Fig. 3.--Section through the nucellus of an ovule of _Melilotus alba_, showing two embryo sacs, one being more advanced than the other. × 360. Fig. 4.--Protoplasm of the pollen mother cell of _Melilotus alba_ contracted and ready to undergo division. × 560. Fig. 5.--Pollen grains of _Melilotus alba_ just formed, showing their dense cytoplasm and the presence of the mother-cell wall. × 560. Fig. 6.--_a_, Mature pollen grain of _Melilotus alba_, showing the binucleate condition at the time of shedding; _b_, surface view. × 560. Plate II. [Illustration] Fig. 1.--Median Section through an Ovule of Melilotus alba. The embryo sac is shown ready for fertilization. The egg and synergids are in contact with the outer integument at the micropylar end. The remains of the antipodals may be seen at the chalazal end. × 180. [Illustration] Fig. 2.--Section through an Ovule of Melilotus alba, about Three Days After Fertilization. The proembryo, the endosperm, and modifications of the integuments are shown. At this stage the suspensor prominent part of the proembryo, and the endosperm is most abundant around the embryo. The inner integument is being rapidly destroyed, and the outer integument is beginning to form the seed coat, as is indicated by the modifications in the outer layer of its cells, which are elongating and thickening their outer walls. × 33. Plate III. [Illustration] Fig. 1.--Section of an Ovule of Melilotus alba after Fertilization. The stage of development is a little later than that shown in Plate II, figure 2. The embryo is embedded deeply in endosperm tissue. × 45. [Illustration] Fig. 2.--Section through an Ovule of Melilotus alba after the Embryo is Nearly Half Mature. But little endosperm remains except in the chalazal end, and very little remains of either the nucellus or inner integument. The modifications which transform the outer integument into a seed coat are well under way. Not only the outer layer of cells which becomes the Malpighian layer is quite well modified, but also the layer beneath is being transformed into the osteosclerid layer. × 30. Plate IV. [Illustration] Stubble of Melilotus alba. These plants, which were cut 12 inches above the ground during rainy weather, had made a 40 to 42 inch growth. The stubble became infected at the top and the light-colored portions of them were killed by disease, thus checking the water supply to the growing branches above the infection. MATURE POLLEN OF SWEET CLOVER.