CELL-CONTENTS AND FORMS OF CELLS. 145 



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

 individuals in compound grains are in some cases easily separated 

 from one another. This occurs frequently in microscopical prep- 

 arations, 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 i ) The shape of the grain, which may be spherical, ellipsoidal, 

 ovoid, polygonal, or of some other characteristic form (Figs. 88 

 and 89). 



(2) The size of the grain, which varies from i to 2 /x to 

 about 100 fi in diameter. 



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

 be central (Fig. 88, C, D) or excentral (Fig. 88, 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 occa- 

 sionally found in potato. 



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

 be spherical, as in potato (Fig. 88, A) ; cross-shaped, as in 

 maranta (Fig. 88, B) ; a three- or five-angled fissure or cleft, as 

 in corn (Fig. 88, D), or indistinct or wanting, as in wheat (Fig. 

 88, C). 



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

 toward the broad end of the grain, as in maranta (Fig. 88, B), 

 or toward the narrow end, as in potato (Fig. 88, A). In most 

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

 (Fig. 88, C,D). 



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

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

 yellowish-red, as in the amylodextrin grains of mace. 



(7) The temperature (45-77 C.) at which the " kleister " 

 or paste is formed, and its consistency. 



(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 (Fig. 91). 



(9) Behavior toward various reagents, as chromic acid, cal- 

 cium nitrate, chlor-zinc-iodide, diastase, and various aniline stains, 

 showing peculiarities of both structure and composition (Fig. 90). 

 General Properties of Starch. If starch is triturated with 

 10 



