SWEET-CLOVER SEED. 29 



Russow (34) concludes that the light line is produced by neither 

 chemical nor mechanical changes but is caused by a modified molec- 

 ular structure containing less water than the remainder of the cell 

 wall. Hiltner (13) agrees with Russow's explanation. Harz (12, 

 p. 561) also agrees with Russow and adds that he has observed that 

 the light line disappeared in a number of cases after applications of 

 nitric acid. Wigand and Dennert (43) suggested that the light line 

 is due to a series of erect fissures, while Tietz (37, p. 32) believes it is 

 due to a chemical modification and that the phenomenon results 

 from the exceptionally extreme density of parts of the cellulose 

 membrane. Junowicz (16) found evidence of cellulose material. 

 The cell wall at this point was strongly refractive and had a different 

 molecular structure. After studying PTiaseolus vulgaris, Haberlandt 

 (7, p. 38) agrees with the Russow explanation. In the seed of this 

 plant the light line colored blue after being treated with chloriodid 

 of zinc. Sempolowski (36), who investigated the light line in Lupinus 

 angustifolius , states that there is not only a difference in the molecular 

 structure but also a chemical modification of the cell wall at this 

 point, since with iodin and sulphuric acid the cell wall colored blue, 

 whereas the light line colored yellow. Wettstein (41), who studied 

 seeds of Nelumbo, agrees with Russow (34) and Sempolowski (36) 

 that chemical and physical modifications occur. He found that iodin 

 and sulphuric acid colored the Malpighian cells intensely blue, the 

 light line at first yellowish, and then later it gradually became blue. 

 This reaction may be accelerated by heat. Iodin produced the same 

 effect, and the light fine colored blue more rapidly. When treated 

 with a water-withdrawing medium the light line was not altered for 

 some time, but finally disappeared with continued application. 

 Cooking for a long time in caustic potash or standing in cold caustic 

 potash caused the cells to swell, while the light line remained unin- 

 jured 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 fight 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 pro- 



