66 



3. Laminae. Indistinct or lacking. 



4. Hilimi. Distinct. 



a. Elongated. 



5. Polarization Crosses. Brilliant and distinct crosses. 



6. Selenite Plate. Fine play of colors. 



D ACORN. 



1. Size. Grains usually 15- — 20/x in diameter. 



a. Few varieties have grains up to 50ju 

 in diameter. 



2. Form. Ellipsoidal. 



a. More irregular than others of this class. 



b. Sometimes in aggregates of few grains. 



3. Laminae. Invisible. 



4. Hilum. Elongated, very distinct. 



5. Polarization Crosses. Very indistinct or not visible. 



6. Selenite Plate. No play of colors. 



V. IRREGULAR GRAINS, (OVOID, PEAR-SHAPED, ROD- 

 SHAPED, ETC.) 



A CURCUMA. 



1. Size. Dependent on the variety. Grains usually GO — 



120^1 long. 



2. Form. Very much elongated Rod-like fomis often 



present. 



a. Blunt point at hilum end. 



3. Laminae. Distinct 



4. Hilum. Small, distinct, in pointed end of grain. 



5. Polarization Crosses. Distinct. 



6. Selenite Plate. Beautiful play of colors. 



B POTATO. 



1. Size. Large grains from 65 — lOO/x long. Seldom larger. 



Very few small grains. 



2. Form. Oyster shell shaped. Sometimes broadly spindle 



shaped. 



a. Aggregates very rare. 



3. Laminae. Very distinct. 



