Bui . 844, U. S. Dept. of Agriculture. 



Plate V. 



/O 



Structure of the Seed Coat of Sweet Clover. 



Fig. 1. — Section of the seed coat of Melilotus officinalis. X450. Fig. 2. — Another section of the seed 

 coat of Melilotus officinalis, showing the variation in size and modifications that occur in the three 

 layers. X450. Fig. 3. — Section of the Malpighian layer of a Melilotus alba seed, showing a line of 

 canals just above the light zone. X450. Fig. 4. — Section of the Malpighian layer of a permeable 

 Melilotus alba seed. X450. Fig. 5. — Tangential section of the Malpighian cells cut between the 

 cuticle and tops of the cones, showing pores. X530. Fig. 6. — Section through the Malpighian layer 

 of an impermeable Melilotus alba seed. X450. Fig. 7. — Section through the Malpighian layer of an 

 impermeable Melilotus alba seed, showing the region through which water and stains readily passed. 

 X450. Fig. 8. — Cross section of a Malpighian cell of a permeable Melilotus alba seed through the 

 region of the light zone, showing the lumen not entirely closed. X530. Fig. 9. — Section through the 

 Malpighian layer of a, Melilotus alba seed shaded to show the portions which react to the cellulose and 

 pectose tests. X450. Fig. 10.— Section through the Malpighian layer of a Melilotus alba seed which 

 shows the condition of the seed coat after 60 minutes' treatment of concentrated sulphuric acid. That 

 portion above the light zone was destroyed, and the lumina as small pores through which much of 

 the stain now passed were seen extending across the light line. The lines between the cells were 

 much more distinct , appearing as small intercellular spaces through which some stain passed. X 450. 

 o, Cuticle; 6, cuticularized layer; c, conelike portion of the thickening of the Malpighian cells; d, 

 light line; e, region of a hard seed coat through which water and stains readily passed, I, lumen; M, 

 Malpighian cells; N, nutrient cells; O, osteosclerid cells; p, canals just above light zone. 



