the cells to swell, while the light line remained uninjured at first but finally disappeared. He also believed that the absence of pore canals in the region of the light line caused it to be more dense. Nobbe and Haenlein (30) treated sections of seed coats of _Trifolium pratense_ with iodin and sulphuric acid and found that the light line colored blue as readily as the thickened ridges that radiate inward from it, but that the outer processes of the palisade cells projecting from the light line toward the cuticle stained dark brown. They also state that various causes work to produce such unusual lusters in the light line, the principle one of which is the thickened ridges which radiate inward, reach their greatest development at this point, and coalesce in the lumen of the cell. The result is that the light line falls upon a continuously homogeneous medium, while in the inner portions of the ridges the light passes through media of varying opacity, such as cellulose, water, and protoplasm, whereby it is progressively subdued in varying degrees by partial reflection. Pammel (31, p. 147) studied the light line in _Melilotus alba_ and found that it consisted of a narrow but distinct refractive zone below the conical layer. The refractive zone colored blue with chloriodid of zinc. The whole upper part was, however, more or less refractive, while the remainder of the cell wall contained pigment and colored blue with chloriodid of zinc. Small canals project into the walls, in some cases extending beyond the light line. Beck (1) found that the light-refracting power of the light line was much greater than that of the undifferentiated membrane and stated that there may be in addition to this a chemical difference which can not be detected with the present microchemical methods. He does not believe that it is cuticularized or that it contains less water than the rest of the cell. Marlière (24, p. 11) gives a physical explanation and states that the true cause of the light line lies in the peculiar structure of the secondary membrane of the Malpighian cell. Tunmann (38, p. 559) observed that it did not hydrolize in weak acids and therefore decided that it was not hemicellulose. He found that it dissolved in concentrated sulphuric acid more readily than the regions surrounding it and that it was composed of pectin or callose. In our investigations the main portion of the light line of _Melilotus alba_ and _M. officinalis_ was very resistant to concentrated sulphuric acid, only the narrow outer portion being attacked. It showed evidence of callose. MATERIAL AND METHODS.