GENUS MUSA. 



775 



Curve of Reaction-Intensities of Starch of Musa 

 sapientum. 



The lamella are very distinct. They are comparatively fine circles immediately around the 

 tiilum. Segments of circles l^eyond show generally a marked tendency to follow the irregularities 

 of the distal margin; those at the distal end are coarser and more distinct than those near the hilum. 

 The number varies in medium-sized and large grains from 48 to 70. 



The grains vary in size from 9 to 70/j. The common size is 46m- 



Polanscopic Properties. The figure is unusually very eccentric, but neither distinct nor clear- 

 cut; its four lines are generallj' broad but of unequal width and length. There is commonly more 

 or less bending and distortion due to variations in width 

 and to irregularities of the grains. 



The degree of polarization is from low to very high 

 in different parts of the grains; as an average fair; on the 

 whole, higher than that of the stalk-starch of M. caven- 

 dishii. There is also not so much variation in the same 

 aspect of a given grain on account of irregularities, hol- 

 lows, and ridges on the surface as in the latter. It is high 

 when the grain is seen from the end or edge, and when 

 there is an overlapping of parts of grains. 



With selenite the quadrants are fairly well defined, 

 but they tend to vary very much in shape and size. The 

 colors are not pure. 



Iodine Reactions. With 0.25 per cent Lugol's solu- 

 tion the grains color immediately and deeply a bluish- 

 violet, more deeply than that of M. cavendishii. With 

 0.125 per cent solution the grains color immediately but 

 lightly and the color deepens quickly until it is some- 

 what deeper than that of the stalk-starch of M. caven- 

 dishii. After heating in water until the grains are com- 

 pletely gelatinized, the solution colors lightly and the grains for the most part deeply on the addition 

 of iodine. The grains are much folded, sacculated, and distorted. Those which do not color deeply 

 show a violet-colored capsule when excess of iodine is added. After boiling for 2 minutes, the solu- 

 tion colors much more deeply and the grain-residues much less. With slight excess of iodine the 

 capsule is colored a blue- violet, and much distorted and crumpled; some contain blue-reacting starch. 



Staining Reactions. With gentian violet staining begins immediately rather lightly; deeper, 

 however, than that with the stalk-starch of M. cavendishii. After 30 minutes the stain is quite 

 deep, especially about the margin and at the distal end. It is much deeper than the stalk-starch 

 of M. cavendishii. 



With safranin staining begins immediately, but after 30 minutes the stain is fairly deep, al- 

 though rather deeper than the stalk-starch of M. cavendishii. The individual gi-ains are stained 

 evenly, but some grains are stained deeper than others. 



Temperature Reaction. The temperature of gelatinization is 67 to 69 C, mean 68. 



Effects of Various Reagents. With chloral hydrate-iodine reaction begins in a minute. Most of 

 the grains are darkened in 3 minutes and all in 7 minutes. The hilum is distinct as a dark spot, but 

 the lamellae are indistinct. The margin darkens at irregular points, usually at the distal end or 

 sides. Frequently the hilum protrudes from the proximal end of the grain at the very beginning of 

 the reaction. The process of swelling and protrusion extends from these points all around the mar- 

 gin, so that an irregular, gelatinized mass surrounds an ungelatinized inner portion, which later 

 is gelatinized. The gelatinized grains so formed are large and very irregular. The distal end shows 

 more or less irregular, broken, concentric, dark semicircles, which are separated by less dark spaces. 

 The upper part shows a dark mass crossed by light fissures. A light-colored saccular protrusion 

 from the distal end of the gelatinized grain represents the swollen grain. 



Reaction with chromic acid begins in 30 seconds and is over in 2 minutes. The hilum is promi- 

 nent and the lamellae are unchanged. The grain becomes divided by fine radial striae and at the 

 same time the hilum protrudes as a small projection from the end of the grain, accompanied often 

 by two or three swellings at nearby points. The whole grain then swells quickly with the formation 

 of a large, thin-walled, gelatinized mass, and at times a collection of coarsely granular material at 

 the distal end. Finally the capsule of the gelatinized grain becomes dissolved at one point, and the 

 inner, granular, gelatinous mass flows out and is dissolved, solution of the capsule following later. 

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