440 



STARCHES OF AKOIDE^. 



STARCHES OF AROIDE/E. 



Chart No. 76. 



Class, Monocotyledoiies. Order, Arales. Family, Aroidea?. Genera repre- 

 sented: Arum, Aristema, Dracunculus, Richardia, Dieffenbachia. 



The AroidecE constitute a large group of tuberous, herbaceous plants, mostly acaulescent, and 

 including about 100 genera and 1000 species. We have studied starches from representatives of 

 5 of these genera. An acrid principle is present in various degrees of abundance or intensity through- 

 out the family, and in some species it is so developed as to render the juice of parts of the plant 

 more or less markedly poisonous. 



GENUS ARUM. 



The genus Anmi is a recognized type of the family of which a number of members are grown 

 under the common name of Calla, though they are not the true Callas, the latter constituting another 

 genus. There are about 50 species, mostly natives of temperate and semitropical Asia. Preparations 

 of starch were obtained from three sources: Anan palccstinvni Boiss. {A. sandutn Hort.), the black 

 calla or Solomon's \\\y;A.cornutuni, a doubtful species; and A. italiann Miller, one of the most variable 

 species. 



STARCH OF ARUM PAL^STINUM. (Plate 13, fige. 77 and 78. Chart 76.) 



Histnlogical Characteristics. In form the grains are simjile, mostly isolated and faceted. They 

 occur rarely in small aggregates, more frequently in large clumps. The facets are very distinct and 

 clear-cut, and somewhat concave. The most conspicuous forms appear to be the dome-shaped 

 and hemispherical, with two or three, or even four, j^ressure facets at the distal end, triangular 

 and spherical. When three or more facets exist thej' are groupetl around a common center. Ovoid, 

 with or without facets, quadrangular, and multiangular 

 forms are seen, and the last are usually very irregular in 

 shape. There are also grains, spherical or ovoid, having 

 both ends flattened by facets. 



The hilmn is a small, fairly distinct, non-refractive 

 spot, usually situated slightly eccentrically; rarely fis- 

 sured, and if a fissure is present, it is neither deep nor 

 wide. At times there is an appearance at the hilum of 

 the existence of a smooth hole. 



The lavK'llod are concentric rings, not very distinct. 

 Sometimes all follow the outline of the margin, and some- 

 times only those near the margin do so. One is, as a rule, 

 much more prominent than the others, and it outlines a 

 small area near by the hilum ; only 8 on one grain could 

 be counted with certainty. 



The grains vary in size from 2 to 20yLi ; common size 

 is 14;;i. 



Polariscopic Properties. The figure is distinct, clear- 

 cut, and regular in shape, and generally slightly eccen- 

 tric. The figure is altered in accord with changes to the 

 shape of the grain. The lines may broaden out as they approach the margin, and become less dis- 

 tinct; or they may be of the same size and distinctness throughout their length. 



The degree of polarization is fair; absent or very low in some of the grains, and in other grains 

 ab.sent only at the facets, where there is a depression. It is lower than in the other Arum starches. 



With selenite the quadrants are well defined, and of nearly the same shape and equal in size 

 in most grains. The colors are not pure. 



Iodine Reactions. With 0.25 per cent Lugol's solution the grains color blue-violet readily 

 and deeply; with 0.125 per cent solution they color less than in A. cornutum. After heating the 

 preparation until all the grains were completely gelatinized, the solution is not colored at all on the 

 addition of Lugol's solution. The gelatinized grains are colored deeply and much distorted and 



PC PS 

 5 



Curve of Reaction-Intensities of Starch of Arum 

 palaestinum. 



