64 



2. Form. Spherical. 



a. Segmented spherical forms rare. 



b. Not found in compact aggregates. 



3. Laminae. Not visible. 



4. Hilum. Central, distinct. 



5. Polarization Crosses. Faint. 



6. Selenite Plate. No play of colors. 



III. CIRCULAR, DISK-SHAPED GRAINS. 

 A RYE. 



1. Size. Grains occur in two sizes: 30 — 60m in diameter 



and 8 — 14ju in diameter. 



2. Form. Large grains circular. 



a. Occur singly. 

 Small grains sphaero-polygonal. 



a. Seldom in aggregates. 



b. More numerous than in other starches 

 of this class. 



3. Laminae. Very distinct. 



4. Hilum. Central, very distinct. 



a. Radiating clefts often present. 



5. Polarization Crosses. Very distinct. 



6. Selenite Plate. Play of colors. 



B WHEAT. 



1. Size. Grains occur in two sizes; 25 — 50^ in diameter, 



and less than Q/j, in diameter. 



2. Form. Large circular flattened grains. 



a. Found singly. 

 Small sphaero-polygonal grains. 



a. Singly or in loose aggregates. 



3. Laminae. Indistinct. 



4. Hilum. Central. 



a. Not usually cleft to any great extent. 



5. Polarization Crosses. Indistinct, (diametrically oppo- 



site.) 



6. Selenite Plate. No play of colors. 



