28 BULLETIN 844, U. S. DEPARTMENT OF AGRICULTURE. 
legumes with concentrated sulphuric acid and obtained a better 
germination in all cases. In their investigations with Melilotus alba 
it was found that a 2-hour treatment resulted in some injury to the 
seed, but that a treatment varying from 25 minutes to 1 hour gave 
good results. In most cases in our investigations the seed coats 
of sweet clover became permeable to water after a treatment of 
15 minutes in concentrated sulphuric acid, and within 5 minutes all 
of the Malpighian cells were destroyed down to the light line. Har- 
rington (10) found that the soil, season, climate, color, or size of 
red-clover seeds had no influence upon the percentage of impermeable 
seeds and that the good germination ordinarily obtained with red 
clover was due to .the scarifying of the seed coats by the rasps of 
hulling machines. Harrington (11) also studied the agricultural 
value of impermeable seeds and found that alternations of tempera- 
ture cause the softening and germinating of many impermeable 
clover seeds when a temperature of 10° C. or cooler is used in alter- 
nation with a temperature of 20° C. or warmer and that the effect 
of such an alternation of temperature is greatly increased by pre- 
viously exposing the seeds to germinating conditions at a temperature 
of 10° C. or cooler and is decreased by previously exposing the seeds 
to germinating conditions at a temperature of 30° C. It is a well- 
known fact that impermeable seeds which remain in the field over 
winter germinate readily the following spring. 
The light line is the most important and interesting feature of the 
Malpighian cell, at least so far as Melilotus alba and M. officinalis are 
concerned. But one light line occurs in the Malpighian cells in 
most Leguminosse, although Pammel (32) reports two well-developed 
light lines in Gymnocladus canadensis, Junowicz (16) found three in 
Lwpinus Varius, and Sempolowski (36) two in Lwpinus angustifolius. 
Many investigators have studied the light line, and different 
theories have been advanced as to its funotion, physical properties, 
and chemical nature. Schleiden and Vogel (35, p. 26) in describing 
the mature testa of Schizolobium excelsum in 1838 undoubtedly referred 
to the light line when they stated that the walls of the Malpighian 
cells were not equally thickened. Mettenius (26), in 1846, was 
probably the first definitely to describe the light line. This author 
believed it was composed of pore canals, all appearing at the same 
height in the cells, but he was unable to prove this by cross sections. 
Lohde (20) studied the light line in seeds of Hibiscus trionum and 
found it cutinized. Hanstein (8) states that the Malpighian cells are 
composed of two cell layers and the light line is produced by the 
adjoining walls of the ends of the cells. Later, this same author (9), 
according to Harz (12), refers to the light line as a perforated disk 
composed of tissue of strong refracting power. 
