63 



2. Form. Sharply polygonal, occasionally sphacro-polygon- 



af. 



a. Rounded ellipsoidal aggregates of usual 

 occurrence. 



3. Laminae. Not evident. 



4. Hilum. Central. (Not always evident.) 



5. Polarization Crosses. Brilliant, distinct crosses. 



6. Selenite Plate. No play of colors. 



II. SPHERICAL AND SEGMENTED-SPHERICAL GRAINS. 

 A SWEET POTATO. 



1. Size. Grains are of two sizes, the larger 25 — 40^t, the 



smaller 5 — 15^ in diameter. 



2. Form. Spherical, with one or two flat sides. 



3. Laminae. Indistinct or lacking. 



4. Hilum. Distinct, excentric. 



a. Excentricity about one-half. 



5. Polarization Crosses. Very distinct, brilliant. 



6. Selenite Plate. Indifferent play of color. 



B CASSAVA. 



1. Size. Grains from 12 — 20 fi in diameter, (seldom reach- 



ing 35m.) 



2. Form. Segmented-spherical. (Kettle-drum shaped.) 



a. Spherical grains rare. 



b. One or two flat sides common, over 

 two rare. 



c. Aggregates of two to five grains some- 

 times found. 



3. Laminae. Very indistinct or lacking. 



4. Hilum. Central, very distinct. 



a. Radiating clefts sometimes present. 



5. Polarization Crosses. Brilliant. 



6. Selenite Plate. Mediocre play of colors. 



C PEANUT. 



1. Size. Grains from 5 — Ion in diameter. (Never larger.) 



