GENUS MUCUNA. 



391 



GENUS MUCUNA. 

 Tho genera Mimina, Vida, Phaseoliis, and Dolichos arc closely allied. Mucuna includes over 

 20 species. M. pruriens DeCand. {Dolichos pruncns Linn., D. muUiJlorus Hort.) is a variable species, 

 and the most prominent representative of the genus. It is popularly known as cow-itch or cow- 

 hage, because of the very marked itching produced when the hairs of the pods penetrate the skin. 

 Starch from this species, probably an agricultural variety, was examined. 



STARCH OF MUCUNA PRURIENS. (Plate 5, figa. 29 and 30. Chart 39.) 



Histological Characteristics. — In form the grains are usually simple, and are isolated, except a 

 small number which occur either in aggregates or as compound grains of few components. The 

 surface of the grains is occasionally marked by a protuberance which is located generally at or 

 near the proximal end. The conspicuous forms are ovoid to oval, nearly round, pyriform, some- 

 times with distal end squared, broadly triangular with curved base and rounded angles. There 

 are some ellipsoidal, bean-shaped, and various incidental forms. 



The hilum is usually fissured, but is sometimes observed as a clear, round or lenticular, refrac- 

 tive spot which is generally about one-sixth eccentric of the longitudinal axis. It may be slightly 

 eccentric or centric in the nearly round grains. At the region of the hilum a very deep, dark cleft 

 often occurs, from which either one oblique, very coarse, dark fissure, or two or more irregularly 

 branched oblique fissures may proceed. Groups of short, irregularly placed, oblique fissures are 

 frequently found, and sometimes the fissuration is of a very diffuse character. 



The lamellw are frequently not demonstrable near or in the region of the hilum, but occasion- 

 ally they may be observed as fine, complete circular or elliptical rings. Those near the margin and 

 distal end are coarse and have the form of the outline of 

 the gi'ain, and in some instances appear to be incomplete. 

 There is frequently one quite coarse, refractive lamella at 

 varying distances from the hilum, which sometimes 

 forms a line of demarcation between the delicate lamel- 

 la? near the hilum and the comparatively coarse lamella) 

 near the margin. On large grains 32 to 40 lamellae can 

 be counted. 



The grains vary in size from the smaller ones, which 

 are 10 by 6^, to the larger, which are 36 by 24/i in length 

 and breadth. The common size is 24 by lifx in length 

 and breadth. 



Polariscopic Properties. — The figure is centric, and 

 usually distinct, but not clear-cut. In the unfissured, 

 elongated grains it consists of a long line bisected at each 

 end and occupying the greater part of the longitudinal 

 axis of the grain. In the fissured grains it is so con- 

 fused by the fissures that there appear to be parts of 

 many figures. In the rounded forms the figure is in the 

 form of a cross. The lines are for the most part thick 

 and straight. Sometimes they are slightly curved and may vary in width between the center of 

 the figure and the margin. 



The degree of polarization is low to high in different grains. It varies also in different aspects 

 of the same grain, being more when the grain is viewed on end or edge. It varies also in some grains 

 in different parts of the same aspect of a grain. 



With selenite the quadrants are generally not sharply defined and are usually unequal in size 

 and irregular in form. In some grains the portions of the quadrants seen are very small. The 

 colors are generally not pure. 



Iodine Reactions. — With 0.25 per cent Lugol's solution the grains color a fairly deep pinkish- 

 violet; with 0.125 per cent solution they color lightly. After heating in water until all of the grains 

 are gelatinized, both the solution and the grains color deeply. After boiling for 2 minutes, the 

 solution colors very deeply and the grain-residues rather lightly. The capsules all color a violet or 

 red-violet with an excess of iodine. 

 27 



Curve of Reaction-Intensities of Starch of 

 Mucuna pruriens. 



