OBNUS DIEFFENBACHIA. 



455 



GENUS DIEFFENBACHIA. 



Dieffenbachia is a genus of tropical and semitropical low perennials, native for the most part of 

 Central and South America. They are in general cultivation as hot-house plants, chiefly because of 

 their fine foliage. There are, according to different authors, from 6 to 12 distinct species. The juice 

 of the plant is very acrid, causing smarting and tingling when applied to the skin, and even much 

 greater irritation when in contact with the mucous membrane. D. seguine Schott is known as 

 "dumb-cane" in the West Indies, because when the root is chewed the tongue swells, interfering 

 with or preventing speech. Starches from four members of the genus, representing two species, 

 were examined, and in each the starches of both pith and cortex were studied separately. The 

 specimens include the following: D. seguine var. nobilis Engl. (D. nobilis Hort.), D. seguine var. 

 niaculata Lowe, D. seguine var. irrorata Engl. (D. irrorata Schott, D. baumanni Hort.), D. illustris 

 Hort. (JD. late-niaculaia Lind. and Andr6). 



PS CI PA 

 "" PC PS 



tA 



STARCH OF PITH OF DIEFFENBACHIA SEGUINE VAR. NOBILIS. 



(Plate 17, figs. 97 and 98. Chart 84.) 



Histological Characteristics. — In form the grains are both simple and compound and show no 

 tendency to form aggregates. The grains originally tend to long, elliptical forms, usually quite 

 regular in outline, but become multiform because of secondary deposits. Plastids may often be 

 seen adhering to some portion or portions of the grains. The forms are very numerous, but the 

 most characteristic is an elongated or flattened ellipse, with one end tending to be round or broadly 

 lanceolate and the other flattened; this may be modified by a bend in the middle of the grain, 

 giving the grain somewhat the shape of a boomerang; or by a bend or protrusion at one end which 

 causes it to assiniie a hook shape. T- and boot-shaped forms are present. The smaller grains 

 are round, ovoid, oval, pyriform, and cylindrical with one end narrower than the other. The pecu- 

 liar T- and boot-shaped and related forms, and the causes of their peculiarities, will be noted partic- 

 ularly in connection with D. seguine var. maculata. The grains of this species bear closer resemblances 

 to D. seguine var. irrorata and D. illustris than to D. seguine var. maculata. On edge, the grains 

 usually appear elliptical, but when seen from the end are round to oval. 



The hilum is a relatively small, round, fairly distinct, non-refractive spot. It is eccentric from one- 

 third to two-fifths of the longitudinal axis of the grain and situated usually in the broader end of the 

 grain, and in or slightly to one side of the median line. Rarely the hilum is double. Fissuration is 

 common, and the fissures are usually ragged and often deep. 



The lamellce are distinct, continuous, fine, regular or 

 irregular circles, ellipses, segments of circles, etc. They 

 vary in size, distinctness, and spacing in the same grain 

 and in different grains. Those added last tend to follow 

 the outline of the margin very closely, and many are some- 

 what wavy. They are flattened in the region distal to 

 the hilum. The boot, T, and transition forms show inde- 

 pendent sets of lamelliE which form the lateral projec- 

 tions, the latter being deposited by plastids after the 

 primary set is completed. These secondary and tertiary 

 sets are added at varying angles to the primary set. In 

 well-developed forms the secondary sets are often the 

 longest and usually coarser and more distinct than those 

 of the primary set. The number of lamella; varies from 

 15 on the small grains to 50 on the large grains. The 

 average is about 35. 



The grains vary in size from 5 to 60^. The common 

 size is 35/i. The largest grains may be from two to six times 

 as long as broad, and about two-thirds as thick as broad. 



Polariscopic Properties. — The figure in the elongated grains is markedly eccentric. It is dis- 

 tinct and the lines are of about the same size and distinctness throughout their length, but may be 

 bent and distorted. Usually but two of the four lines are visible for any length, the other two being 

 very short. Various modifications are shown in part in the photographs. 

 31 



Curve of Reaction-Intensities of Starch of Dieffcnbacki« 

 seguine var. nobilis (pith). 



