GENUS QtTERCUS. 



421 



STARCHES OF CUPULIFER/E. 



Class, Monocotyledones. Order, Fagales. Family, Cupulifera). 

 represented: Quercus, Castanea. 



Genera 



The Cupuliferce include a number of important exogenous trees such as the oak, chestnut, and 

 beech. The family embraces 10 genera and 368 recognized species. 



GENUS QUERCUS. 



The oaks are widely distributed in the temperate and cool temperate regions of the Northern 

 Hemisphere, in the mountainous parts of Mexico and Central America, and in the mountains of 

 Central and Eastern Asia. They are absent south of the Mediterranean region, and also south of 

 the equator in the New World. The genus includes about 300 species, about 40 of which are found 

 in the United States — 25 east of the Rocky Mountains. A number of hybrids have been recorded. 

 The species have been divided into subgenera, but except Q. densiflora (peach oak of California) all 

 the American and European species belong to the subgenus Lepidobalamis. The acorns, or fruits, 

 of 5 species were used as sources of starches, as follows: Q. alba Linn., the white oak; Q. muehlenhergi 

 Engelm. (Q. castanea Willd.; Q. acuminata Sarg.; Q. prinus var. acuminata Michx.), the yellow 

 chestnut oak; Q. prinus Linn. {Q. prinus var. monticola Michx.; Q.montanaWiUd.), the chestnut 

 oak or rock chestnut oak; Q. rubra Linn. (Q. ambigua Michx.), and the red oak, Q. texana Buckl., 

 the Texan red oak or Spanish oak. 



STARCH OF QUERCUS ALBA. (Plate 11, figs. 61 and 62. Chart 64.) 



Histological Characteristics. — In form the grains are generally simple, and they are isolated, 

 except some which occur in clumps, small aggregates, or compounds which usually consist of two 

 components. A few of the isolated grains have clearly 

 marked pressure facets. The conspicuous forms are ellip- 

 soidal, somewhat bean-shaped, pyriform, ovoid, and len- 

 ticular. There are some triangular with rounded angles, 

 hemispherical, sugar-loaf, nearly round, finger-shaped, 

 and indefinite forms. The surface of the grains is fre- 

 quently irregular, owing chiefly to wart-like excrescences 

 at one or more points. These additional growths are 

 generally located at either end of an ellipsoidal or nearly 

 round grain, and are usually less resistant to reagents 

 than the main portion of the grain. 



An elongated cleft, with or without radiating fissures, 

 is most frequently found at the hilum. Occasionally in 

 the ellipsoidal, pyriform, and nearly round grains the 

 hilum appears as a clear, round eccentric spot, from which 

 one longitudinal fissure often proceeds. There may also 

 be present at the hilum in such grains a nearly round 

 cavity, a cross, or a Y-shaped figure. The hilum may 

 rarely be observed as a clear, round, or lenticular cavity, 

 usually two-fifths to one-third eccentric. 



The lamellce are not visible in most of the grains, but when seen are rather coarse, complete 

 rings which, even near the hilum, have the form of the margin of the grain. In grains of common 

 size eight to ten have been counted. In some of the most irregular grains secondary sets of lamellae, 

 more indistinct than the primary lamellee, may be observed. 



The grains vary in size from the small, which are 4 by Zn, to the larger, which are 32 by 14^* 

 in length and breadth. The common size is 22 by 12/ii. 



Polariscopic Properties. — The figure is usually more or less eccentric. In most grains it is either in 

 the form of a longitudinal line having bisected ends, or a cross having lines which intersect at right or 

 oblique angles. The figure is distinct, and frequently irregular, and the lines are often bent or bisected. 



Curve of Reaction-Intensities of Starch of Quercus alba. 



