MORPHOLOGY 



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of a flattened sphere or ellipsoid ; they show a distinct stratification, 

 and are crossed by fissures radiating from the centre. The disc-shaped 

 starch grains of wheat are of unequal size, and only indistinctly strati- 

 fied (Fig. 65). A comparison of the accompanying figures (Figs. 72- 

 75), all 'equally magnified, will give an idea of the varying size of 

 the starch grains of different plants. The size of starch grains 

 varies, in fact, from 0'002 mm. to 0'170 mm. Starch grains O170 

 mm. large, such as those from the rhizome of Canna, may be seen 

 even with the naked eye, and have the appearance of brilliant points. 

 In addition to the simple'starch grains so far described, half-compound 



Fig. 75. — Starch grains of wheat. 

 Tritieum duruvi. A, Large 

 B, small grains. ( x 540.) 



Fig. 74. — Starch 

 grains from the 

 cotyledons of 

 Phaseolus vul- 

 garis. (X 540.) 



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Fig. 76. — Starch grains of oats, 

 Av&na sativa. A, Compound 

 grain ; B, isolated component 

 grains of a compound grain. 

 (X 540.) 



Fig. 77. — Leucoplasts from an aerial tuber 

 of Phajus grandifolius. A, C, B, E, 

 Viewed from the side ; B, viewed from 

 above ; E, leucoplast becoming green 

 and changing to a chloroplast. ( X 540.) 



and compound starch grains are often found. Grains of the former 

 kind are made up of two or more individual grains, surrounded by 

 a zone of peripheral layers enveloping them in common. The com- 

 pound grains consist merely of an aggregate of individual grains un- 

 provided with any common enveloping layers. Both half-compound 

 (Fig. 73, B) and compound starch grains (Fig. 73, C, D) occur in 

 potatoes, together with simple grains. In oats (Fig. 76) and rice all 

 the starch grains are compound. According to Nageli, the compound 

 starch grains of rice consist of from 4 to 100 single grains; those of 

 Spinacia glabra sometimes of over 30,000. Starch thus formed from 

 previously assimilated organic substances also requires chromatophores 

 for its production. It is produced by means of leucoplasts, which are, 

 in consequence, often termed starch-builders. If the formation of a 

 starch grain should begin near the periphery of a leucoplast, the grain 

 would eventually, by its continued enlargement, protrude from the 

 leucoplast. As new layers of starchy matter are then deposited only 



