CELL CONTEXTS 



185 



In some forms — e.g., belladonna root (Plate 75, Fig. 2) the 

 compound grains are more numerous; while in sanguinaria the 

 simple grains are more numerous, etc. 



OUTLINE 



The outline of starch grains is made up of (1) rounded, (2) 

 angled, and (3) rounded and angled surfaces. 



Starch grains with rounded surfaces may be either spherical, 

 as in Plate 74, Fig. 3, or oblong or elongated, as in Plate 71, 

 Fig. 1. 



Other starches with rounded surfaces are shown on Plates 

 72 and 73. 



Angled outlined grains are common to cardamon seed, white 

 pepper, cubebs, grains of paradise (Plate 76, Fig. 4), and to corn 

 (Plate 70, Fig. 3). 



The outlines of all compound grains are made up partly of 

 plane and partly of curved surfaces. 



SIZE 



The size (greatest diameter) of starch varies greatly even 

 in the same species, but for each plant there is a normal variation. 



In spherical starch grains the size of the individual grains is 

 invariable, but in elongated starch grains and in parts of com- 

 pound grains the size will vary according to the part of the grain 

 measured. In zedoary starch (Plate 71, Fig. 4), for instance, 

 the size will vary according to whether the end, side, or surface 

 of the starch grain is in focus. 



The parts of compound grains often vary greatly in size. 

 Such a variation is shown in Plate 75, Fig. 2. 



HILLTM 



The hilum is the starting-point of the starch grain or the 

 first part of the grain laid down by the amyloplast. The hilum 

 will be central if formed in the middle of the amyloplast, and 

 excentral if formed near the surface of the amyloplast. It 

 has been shown that the developing starch grain with eccentric 

 hilum usually extends the wall of the amyloplast if it does not 

 actually break through the wall. Starch grains with excentral 

 hilums are therefore longer than broad. 



