i64 BOTANY AND PHARMACOGNOSY. 



nate lamellae are stained by the use of gentian violet and other 

 aniline dyes, which may be taken to indicate that these layers 

 contain a colloidal substance somewhat resembling a mucilage, 

 while the alternating layers are stained with dilute iodine solu- 

 tions and are probably composed of soluble starch, this latter cor- 

 responding to the a-amylose of Arthur Meyer or the granulose 

 described by Nageli. The peripheral layer of the grain appears 

 to be a distinct membrane. It is quite elastic, more or less porous, 

 and takes up stains readily. 



While starch grains usually 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 character- 

 istics : 



(i) 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 i or 2 a 

 to about 100 iJ- 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. 316,0. 



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

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

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



