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 line 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 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 pro- 
