BEGONIA. 



709 



and any irregularities that may occur are due to the 

 following causes : ( 1 ) A secondary set of lamellae whose 

 longitudinal axis is usually at a right angle to that of 

 the primary set; (2) rarely, 1 or 2 rounded protu- 

 berances from the proximal end; (3) 1 or 2 pressure 

 facets on the smaller grains; (4) rarely, a slight devia- 

 tion of the axis and consequent bending of the grain. 

 The conspicuous forms are ovoid, elongated elliptical, 

 round and nearly round, and triangular. The additional 

 forms are dome-shaped and pyriform. The grains are 

 usually not flattened, but the few broad forms are some- 

 what flattened and when seen on edge have an elongated 

 elliptical or ovoid shape. 



The hilum when not fissured is a rather indistinct, 

 small, round spot. It is fissured in a small majority 

 of the grains and the fissures are very small and not deep. 

 They have the following forms: (1) A small, straight, 

 transverse or oblique line; (2) cruciate, T- or Y -forms; 

 (3) an irregularly stellate arrangement or fissures; (4) 

 a flying-bird. The hilum is eccentric from 0.44 to 0.12, 

 usually 0.25, of the longitudinal axis. 



The lamella are usually fine, regular, and moderately 

 distinct. Near the hilum, they are round or oval in 

 form and continuous, and in the rest of the grain, down 

 to the margin, they are regular but discontinuous and 

 have the form of the outline of the grain. There is often 

 1 broad refractive lamella near the hilum and, if the 

 grain contains both primary and secondary starch, broad 

 refractive lamellae surrounding the primary grain ; while 

 there are often 3 or 4 other coarse lamella? from about the 

 upper one-third to the margin which divide the fine 

 lamella? into bands of varying breadth. The lamella? of 

 the secondary starch are not so fine and are more distinct 

 than those of the primary deposit. The number counted 

 on the larger grains varies from 18 to 40, usually 36, less 

 than in B. socotrana. 



In size the grains vary from the smaller which are 

 4 by 4/i, to the larger which are 44 by 24/t, rarely 50 by 

 26/i, in length and breadth. The common sizes are 22 by 

 18/i and 24 by 14/*. 



Comparison of the histologic properties between B. 

 socotrana and B. double white shows : 



Form : — Compound grains and aggregates which 

 occur occasionally in B. double white are not seen at all in 

 B. socotrana. The grains of B. socotrana are more 

 irregular than those of B. double white, and the irregu- 

 larities are due to the following causes: (1) 1 or more 

 large rounded protuberances from the proximal end and 

 sides; (2) a greater development of one part of the distal 

 end than the rest; (3) a deviation of the axis and con- 

 sequent bending of the grain; (4) rarely, regular ele- 

 vations and depressions in the distal end producing a 

 fluted appearance; (5) rarely, a secondary set of lamella? 

 whose longitudinal axis is at an angle to that of the 

 primary set. The first of these causes is but rarely seen 

 in B. double white, the second and fourth are never seen, 

 and the fifth (which occurs but rarely in B. socotrana) 

 is the most common cause of irregularity in B. double 

 white. In form the grains are much more often elon- 

 gated, comparatively few of the round or triangular 

 forms being seen. 



The hilum is somewhat less distinct and is much less 

 often fissured. The fissures have only three forms: (1) 

 As in B. double ivhite, a single, straight, rarely curved 



line, transversely or obliquely placed; (2) a somewhat 

 branched Y form, but no cruciate or T forms such as 

 occur in B. double white are seen; (3) as in B. double 

 white, an irregularly stellate arrangement of fissures. 

 The hilum usually is 0.18 of the Longitudinal axis, which 

 is 0.07 more eccentric than in l'>. double white. 



The lamella? are not so distinct and arc usually finer 

 than in B. double white. There is never a broad, dlstini I 

 lamella very near the hilum, nor a distinct lamella sepa- 

 rating the primary from the secondary starch in grains 

 which consist of both primary and secondary starch. 

 Otherwise the arrangement is the same They are often 

 not regular, as in B. double white, but show a waviness of 

 outline. 



In size the grains are somewhat larger and more 

 slender, the larger grains being 2/i longer and 2/i narrower 

 than the largest grain measured in B. double while. 

 The common sizes are, respectively, 8/t longer and the 

 same breadth, and 8/i longer and 3/i broader, than the 

 corresponding common sizes of B. double white. 



Polariscopic Properties. 



The figure is distinct and moderately well-defined. 

 The lines are fine, as a rule, and cross at a right angle 

 or at an acute angle which varies somewhat in size in the 

 different grains. They are often somewhat bent and 

 moderately often bisected. 



The degree of polarization varies from low to moder- 

 ately high (value 55). In most grains it is moderate, 

 in a few it is low, and in a few moderately high. There 

 is often some variation in a given aspect of an individual 

 grain. 



With selenite the quadrants are moderately clear-cut. 

 They are usually unequal in size and often irregular in 

 shape. The colors are usually not quite pure. 



Comparison of the polariscopic properties between 

 B. socotrana and B. double white shows: 



The figure is as distinct and usually better defined. 

 The lines are not so fine and usually cross at an acute 

 angle which does not vary so greatly in size in different 

 grains. They are less often bent or bisected than in B. 

 double white. 



The degree of polarization varies from moderate 

 to moderately high (value 60), 5 units more than in 

 B. double white. There is less often variation in a given 

 aspect of an individual grain. 



With selenite the quadrants are more clear-cut, they 

 are more unequal in size, and more regular in shape than 

 in B. double white. The colors are more often pure and 

 there are some which show a greenish tinge. 



Iodine Reactions. 

 With 0.25 per cent LugoFs solution the grains all 

 color a light violet (value 25). The color deepens slowly 

 until it is moderately deep and has assumed a somewhat 

 bluish tint. With 0.125 per cent LugoFs solution the 

 grains all color very lightly, and the color deepens slowly 

 until it is moderate and has assumed a somewhat bluish 

 tint. After heating in water until the grains arc all 

 gelatinized and then treating with a 2 per cent LugoFs 

 solution, the gelatinized grains are all colored a moderate 

 indigo, and the solution a deep indigo. If the prepara- 

 tion is boiled for 2 minutes and then treated with an 

 excess of a 2 per cent LugoFs solution, the grain-residues 



