GENUS QUERCUS. 



423 



the region of the hilum. Gclatinization and a rapid distension of the capsule now begins, usually 

 at both ends of the bcan-shajiod and lenticular forms and at the distal end of the pyriform and 

 other grains having a demonstrable, eccentric hilum. The central portion is the last to undergo 

 gelatinization. Gradually, however, pieces are broken off from this more resistant starch and gelat- 

 inized, until the entire grain is gelatinized. The swollen grain is much distorted and therefore 

 does not retain the shape of the untreated grain. 



The reaction with Purdy's solution begins immediately. A few grains are gelatinized in 30 

 seconds, the majority in a minute, nine-tenths in 2 minutes, and all but a very few resistant forms 

 (one in several hundred) in 3 minutes, most of the latter being gelatinized usually in 5 minutes, 

 extremely few as late as 15 minutes. The cleft at the hilum, or the hilum, swells, and the lamellae be- 

 come sharply defined and striated. From the central cleft numerous delicate lines radiate, along the 

 course of which gelatinization proceeds. When an eccentric hilum is demonstrable, a longitudinal 

 refractive line with nimierous branches extends from it towards the distal end of the grain, and the 

 starch is gelatinized along this root-like fissure until most of the grain is gelatinized. If a grain 

 has one or more excrescences, a focus of gelatinization occurs in each of these portions, as well as in the 

 body of the grain, and a line of demarcation may remain between the separate sections of the grain, 

 which sections subsequently become gelatinized. When the line of division does not gelatinize it 

 may indicate the presence of a compound grain, even though separate hila were not demonstrable 

 in the untreated grain. This separation is not so sharply marked as in doublets, because here a 

 common lamellar covering incloses the divisions. The large grains mth irregular outline gelatinize 

 more rapidlj' than the others, and the contents of the capsule usually become completely gelatin- 

 ized; while the grains in which the reaction is slower retain many refractive granules and often 

 a few remnants of ungelatinized lamella?. The gelatinized grain is large and somewhat distorted, 

 but retains the general shape of the untreated grain. 



STARCH OF QUERCUS MUEHLENBERGI. (Plate 11, figs. 63 and 64. Chart 65.) 



Histological Characteristics. In form nearly all of the grains are simple. Doublets and triplets 

 and also compound grains, consisting usually of two components, are rarely observed. The simple 

 grains are isolated, except a few which occur either in small aggregates or clumps. The conspicuous 

 forms are the same as those noted for Q. alba, but ovoid, ellipsoidal, and pyriform shapes constitute a 

 lai'ger percentage of the grains. On the other hand, the 

 grains with protuberances of characters similar to those 

 noted under Q. alba, while present, are not so numerous, 

 and hence the surface of the grains, as a whole, appears 

 less irregular. Fewer aggregates are found than in Q. alba. 



The hilum is often observed as a round, rarely len- 

 ticular, cavity, usually about one-third to two-fifths 

 eccentric. From the hilum a longitudinal cleft frequently 

 proceeds. This cleft is usually single and clear-cut, but 

 occasionally ragged or double, and a few radial fissures 

 may emerge from it. Just below the hilum a crescentic 

 or a straight transverse fissure may be found, which with 

 the longitudinal fissure already described forms a cross. 

 In the bean-shaped grains a cleft similar in character to 

 that noted under Q. alba is observed, but the central 

 clefts of the grains are not so deep, and the hilum is 

 more often demonstrable than in Q. alba. 



The lamellce are not demonstrable in all the gi-ains, 

 and when observable are less easily traced near the hilum 

 than when near the periphery, on account of the cleft 

 at the hilum. The lamellae appear as rather coarse, concentric layers with an outline similar to that 

 of the margin of the grain. The number counted on different grains varies from 6 to 10. 



The size varies from the small, globular grains, which are 4 by 3ai, to the larger elongated forms, 

 which are 30 by 19/n in length and breadth. The common size is 16 by 10/i. 



Polariscopic Properties. The figiire is usually eccentric, distinct, and fairly clear-cut. Several 

 grains show the pecuUar bean type of figure noted in Q. alba. The lines of the figure are often 

 29 



I QV T P 

 S 



Chart No. 65. 



CA PA FC P 5 CI PA CA 



Curve of Rcaclion-Intenaitiea of Starch of 

 Quercus muehlcnbcrgi. 



