464 



STARCHES OF AROIDE^. 



larly granular, and the margin shows fine striae, especially near the hilum. Two kinds of gelat- 

 inized grains are formed according to the two modes of swelling: one triangular with a base cor- 

 responding to the distal end and the apex to the hilum, the other irregularly elliptical, lobulated, 

 and folded. 



Reaction with Purdy's solution begins in one-third of the grains in 2J^ minutes and all are par- 

 tially gelatinous in 1}^ hours. Both hilum and lamella' become very distinct. The distal end may 

 begin to swell, or two refractive lines may start from the hihun, outlining an inner portion. Longi- 

 tudinal fissures extend upward from the distal end, and these with transverse fissures separate the 

 granules thus formed into rows corresponding to the lines of lamellse. The longitutlinal fissures 

 at times may extend part way from the proximal end, leaving the distal portion unstriated. The 

 inner granular portion passes into a gelatinous mass and the more resistant starch at the margin 

 forms a wide, finely striated band marked by refractive and non-refractive lines. This liand 

 gradually becomes clearer and thinner until it is transformed into a thin envelope or capsule. The 

 grains are large, generally more or less oval, and somewhat lobulated and fokled. 



STARCH OF CORTEX OF DIEFFENBACHIA SEGUINE VAR. IRRORATA. 



(Plate 18, figs. 107 and 108. Chart 89.) 



Histological Characteristics. In form the grains are both simple and compound, and thej' are 

 isolated. The most conspicuous form is flattened ellii)tical, the distal end tending to be pointed. 

 A chloroplastid may be made out, occasionally adhering to the grain at the distal end. In some of 

 these forms both ends may be rounded and nearly equal in size, or both may be pointed, owing 

 probably to the beginning of erosion; or the proximal end may be narrower than the distal end. 

 Other elongated forms include short or broad, hook-shaped, T-shaped, boot-shaped, and various 

 irregular shapes due mostly to secondary deposits of lamellae. The proportion of grains of freakish 

 shapes due to secondary lamellae is notably less than in 

 other starches of this genus, particularly in comparison 

 with D. seguine var. maculala. From the end the elliptical 

 grains appear round or oval, or occasionally somewhat 

 prismatic. Usually they are not so thick as broad. The 

 grains as a whole are smaller and less wide in proportion 

 to length than in the pith starch. 



The hihan is a fairly distinct, small, round, non- 

 refractive spot, eccentric in the elliptical grains about 

 two-fifths of the longitudinal axis of the grain, and situ- 

 ated in the median line. It was never seen to be fissured 

 or to be double or multiple. 



The lamellcE are fairly distinct, regular or irregular 

 rings or ellipses, or segments of ellipses or rings, some- 

 times flattened at the distal end or wavy. The lamellae 

 around the hilum are circular, but beyond this they tend 

 to follow the outline of margin of distal end. The T-shaped 

 and other grains having secondary deposits show one or 

 two additional sets, as in the case of grains of these types 

 in other Dieffenbachia starches. They vary in size, dis- 

 tinctness, and spacing, those near the distal end being larger, further apart, and more distinct. The 

 smaller grains have much finer and less distinct lamellae than the larger grains, and the secondary 

 lamellae are coarser than the primary, varying from 10 on the small to 44 on the large grains; the 

 average is about 30. 



The size of the grains varies from 4 to 47^. The common size is 27/i. 



Polariscopic Properties. The figure in the elongated grains is very eccentric and well defined, 

 lines usually narrow and not clear-cut. In the few grains of the round or ovoid type the figure is 

 centric or nearly centric, and in the form of or ap])roaching that of a cross. 



The degree of polarization is fair, distinctly lower than in the pith starch, highest when the grain 

 is viewed from the end or edge, and varying distinctly in different grains. 



With selenite the quadrants are usually fairly well defined, very unequal in size, and variable 

 in shape. The colors are fairly pure. 



Curve of Reaction-Intensities of Starch of Dieffenbachia 

 seguine var. irrorata (cortex). 



