i64 BOTANY AND PHARMACOGNOSY. 



While starch grains usuahy occur singly, they are not infre- 

 quently found in groups of two, three or four grains, when they 

 are spoken of as two-, three-, or four-compound. In some of the 

 cereals, as rice and oat, they are lOO-compound or more. The 

 individuals in compound grains are in some cases easily sepa- 

 rated from one another. This occurs frequently in microscopical 

 preparations, and is especially noticeable in the commercial 

 starches. 



The various commercial starches belong to the class of reserve 

 starches and may be distinguished by the following characteristics : 



( 1 ) The shape of the grain, which may be spherical, ellip- 

 soidal, ovoid, polygonal, or of some other characteristic form 

 (Figs. 316, 317). 



(2) The size of the grain, which varies from 1 or 2 fi 

 to about 100 fj. in diameter. 



(3) The position of the point of origin of growth, which may 

 be central (Fig. 316, C, D) or excentral (Fig. 316, A, B). 

 In some cases there are apparently two points of origin of growth 

 in a single grain, and it is then spoken of as " half-compound," 

 as in potato (Fig. 316. A). 



(4) The shape of the point of origin of growth, which may 

 be spherical, as in potato (Fig. 316, A) \ cross-shaped, as in 

 maranta (Fig. 316, B) ; a three- or five-angled fissure or cleft, 

 as in corn (Fig. 316, D), or indistinct or wanting, as in wheat 

 (Fig. 316, C). 



(5) The convergence of the lamellae, which may be either 

 toward the broad end of the grain, as in maranta (Fig. 316, 5), 

 or toward the narrow end. as in potato (Fig. 316, A). In most 

 grains the lamellae are indistinct or wanting, as in wheat and corn 

 (Fig. 316, C, D). 



(6) Behavior toward dilute iodine solutions, the color pro- 

 duced varying from a deep blue in most starches to a red or yel- 

 lowish red, as in the amylodextrin grains of mace. 



(7) The temperature (45-// C.) at which tlie " kleister " 

 or paste is formed, and its consistencv. 



(8) The appearance as viewed by polarized light, the distinct- 

 ness of the cross, as well as the degree of color produced, varying 

 considerably as Nichol's prism is revolved (Figs. T75a, 322), 



