GENERA PHASEOLUS AND DOLICHOS. 



389 



Differentiation of Certain Starches 



POLARISCOPIC PUOI'EKTIES. 



Figure. 



P. vtitddria: Contric, or sliRhfly crrentrio, distinrt, usually 

 clear-cut, regular, coininonly a single mesial line 

 bisected at each end. 



P. lunatus: Same as in P. vulgaris. 



Degree of Polarization. 



P. vulgaris: High. 



P. lunatus: High, slightly less than in P. vulgaris. 



Polarization with Sdeiiite Qiinilranls and Colors. 



P. vulgaris: Quadrants well-defined, generally irregular, 

 unequal in size, and sometimes subdivided. Colors 

 usually pure. 



P. lunatus: Same as in P. vulgaris. Colors usually pure. 



Iodine Reactions. 



Intensity and Color. 



P. vulgaris: Fairly deep; blue to pinkish-violet. 

 P. lunatus: Fairly deep, slightly less than in P. vulgaris; 

 blue to pinkish-violet. 



Staining Reactions. 



With Gentian Violet. 



P. vulgaris: Light. 



P lunatus: Light, slightly less than in P. vulgaris. 



With Safranin. 

 P. vulgaris: Light. 

 P. lunatus: Light, slightly less than in P. vulgaris. 



Temperature op Gelatinization. 



P. vulgaris: 74 to 75 C, mean 74.5. 

 P. lunatus: 79 to S0 C, mean 79.76. 



of the Genus Phaseolus. Continued. 



Effects of Various Reagents. 



Reaction with Chloral Hydrate-Iodine. 



P. vulgaris: Begins in a few in 20 seconds; complete in 

 one-fifth in 30 minutes, and in two-fifths in an 

 hour. 



P. lunatus: Begins in a few in 30 seconds; complete in 

 two-fifths in 30 minutes, and in half in an hour. 



Reaction with Chronic Acid. 



P. vulgaris: Begins in most in 1 to 2}4 minutes; com- 

 plete in all in 8 minutes. 



P. lunatus: Begins in most in 1 to 2 minutes; complete 

 in all in 8 minutes. 



Reaction with Pyrogallic Acid. 



P. vulgaris: Begins in all in a minute; com|)lcte in all 



in 5 minutes. 

 P. lunatus: Begins in most in a minute; comiilete in all 



in 4 minutes. 



Reaction with Ferric Chloride. 



P. vulgaris: Begins in a few in 2J^ minutes; complete 



in a very few in 30 minutes; no further reaction 



in an hour. 

 P. lunatus: Begins in a few in 2 minutes; complete in 



one-third in 50 minutes; no further reaction in an 



hour. 



Reaction with Purdy's Solution. 



P. vulgaris: Begins in some in a minute; a few are 



partially gelatinized in 20 minutes, no further 



reaction in an hour. 

 P. lunatus: Begins in some in 1 minute; about one-fourth 



are nearly comijletely gelatinized in 45 seconds, 



no further reaction. 



NOTES ON THE STARCHES OF PHASEOLUS. 



These starches do not exhibit any notable differences in their gross histological characters 

 except that in P. vulgaris fissuration appears to be more marked and the lamella; somewhat less 

 distinct than in P. lunulus. In comparing the reaction-curves it will be seen that P. vulgaris has a 

 higher degree of polarization, greater responsivity with iodine, anilines, and heat; somewhat less 

 responsivity to chloral hydrate-iodine, pyrogallic acid, ferric chloride, and Purdy's solution; and 

 the same reactiveness with chromic acid. The most marked differences are in the temiieratiu'cs 

 of gelatinization, the starch of P. vulgaris being gelatinized at 74.5 C, and that of P. lunatus at 

 79.75, a difference of 5.25. The differences apart from the temperature reactions arc unimportant. 



GENUS DOLICHOS. 



The genus Dolichos, which is closely related to Pliaseolus, includes about 50 species, several of 

 which are in common cultivation. The best knowai is D. lablab Linn. (D. cuUratus Thumb., D. pur- 

 purcus Lindl.), the hyacinth, EgyiJtian, or black bean. The starch of this species was studied as the 

 type of the genus. 



STARCH OF DOLICHOS LABLAB. (Plate 6, figs. 35 and 36. Chart 38.) 



Histological Characteristics. In form the grains are simple, although peculiarities of fissuration 

 make some of them appear as compounds. The surface of the grains is usually somewhat regular, 

 the irregularities being due to low, rounded prominences or slight depressions of the margin. The 

 conspicuous forms are the ovoid to oval and elliptical, and nearly round, with some triangular 

 with rounded angles and rounded base, a few bean-shaped, quadrangular with rounded angles, 

 and various modifications of the foregoing. The grains are generally about two-thirds as thick 

 as they are broad. 



