D1V. I 



MORPHOLOGY 



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 O'lTO 



FIG. 26. Starch grains from the 

 cotyledons of Phaseolus rul- 

 garis. (x 540. After STRAS- 

 BURGER.) 



f? 



FIG. 25. Starch grains from a potato. A, simple; 

 B, half- compound ; C and D, compound starch 

 grains ; c, organic centre of the starch grains. 

 ( x 540. After STRASBURGER.) 



FIG. 27. Starch grains of the oat, 

 Arena sativa. A, Compound 

 grain ; B, isolated component 

 grains of a compound grain. 

 (x 540. After STRASBURGER.) 



mm. Starch grains O'lTO mm. large may be seen even with the 



naked eye, as minute bright bodies. The starch grains stored as 



reserve material in potatoes are comparatively large, attaining an 



average size of 0'09 mm. As shown in the above figure (Fig, 25 A), 



they are plainly stratified. The stratification is due to the varying 



densities of the successive layers ; 



thicker denser layers which appear 



clear by transmitted light alternate 



with thinner less dense layers which 



appear dark. They are excentric in 



structure, since the organic centre, 



about which the different layers are 



laid down, does not correspond with 



the centre of the grain but is nearer 



to one margin. The starch grains of 



the leguminous plants and cereals, on 



the other hand, are concentric, and 



the nucleus Of their formation is in FlG . 2S.-Leucoplasts from an aerial tuber 



the centre of the grain. The starch 



grains of the kidney bean, Phaseolus 



ruh/aris (Fig. 26), have the shape of 



flattened spheres or ellipsoids ; they 



show a distinct stratification, and are crossed by fissures radiating 



from the centre. The disc-shaped starch grains of wheat are of 



of Phajiis g randifol i us. A , C, D, viewed 

 from the side ; B, viewed from above ; 

 st, starch grain ; kr, proteid crystal, 

 (x 540. After STRASBURGER.) 



