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.
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.
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.