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 Leguminosae, although Pammel (32) reports two well-developed 

 light lines in Gymnocladus canadensis, Junowicz (16) found three in 

 Lupinus varius, and Sempolowski (36) two in Lupinus angustifolius. 



Many investigators have studied the light line, and different 

 theories have been advanced as to its function, physical properties, 

 and chemical nature. Schleiden and Vogel (35, p. 26) in describing 

 the mature testa of Scliizolobium 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. 



