892 



STARCHES OF CYCADACE^. 



STARCHES OF CYCADACE/E. 



Class, Gymnospermse . Order, Cycadales. Family, Cycadacese. 

 represented: Cycas, Dioon, and Zamia. 



Genera 



Chart No. 394. 



The GynmospermcB are regarded by some authors as a subclass of Dicotyledones. Of the three 

 orders of this class (Gnetacem, Coniferacece, and Cycadacea) the starches of representatives of only 

 Cycadacece were examined. This peculiar order has affinities with the ferns, but resembles the 

 palms, and its sexual characters are transitional between angiosperms and vascular cryptogams. 

 There are recorded 9 genera and 75 species of Cycadacece; Cycas is the chief genus and includes 

 about 20 species, several of which are quite widely cultivated. 



GENUS CYCAS. 



The various species of Cycas are widely distributed throughout the tropical and subtropical 

 parts of the Eastern hemisphere. Starches from the side-shoots of two species were studied: C. 

 revoluta Thunb., the sago palm, a native of Japan and China, and the most common Cycad in cul- 

 tivation; and C. drcinalis Linn. (C. thouarsii T. Br.), a native of the East Indies to New Guinea. 



STARCH OF CYCAS REVOLUTA. (Plate 101, figs. 603 and 604. Chart 394.) 



Histological Characteristics. In form the gi-ains are simple. There are a few aggi-egates and 

 clumps. Most grains have pressure facets, which rarely exceed three on a single gi-ain, although four 

 or five may occiu". Occasionally three facets are grouped about a common center at the base of the 

 grain and are usually sharply defined. The fundamental 

 form of the grain is obviously spherical, and any modi- 

 fications of this are due to the mutual pressure of grains. 

 The small grains are generally spherical. The conspicu- 

 ous forms are the hemispherical to dome-shaped with one 

 to three facets at the base, round or nearly round, and 

 ovoid. Various polygonal and indefinite forms owe their 

 peculiarities chiefly to the presence of many facets. 



The hilum is a distinct, non-refractive, round spot of 

 medium size, in most cases having the appearance of a 

 round cavity communicating with the interior of the 

 grain. It is placed centrally or very slightly eccentric- 

 ally, and usually in the median line. Occasionally it is 

 transversely fissured, but not extensively, and there may 

 be a longitudinal or a 3-armed fissure. In one case a 

 double, or ijo.ssibly an elongated, hilum was noted. 



The lamella are usually distinct, regular, concentric 

 rings. Those near the margin tend to follow the marginal 

 outline. In some of the larger and round types, one or 

 two of the prominent, inner lamellse show distorted areas which apparently are the remains of old 

 pressure facets that have been covered by layers of starch. Some of the lamellse are broader and 

 more distinct than others, especially those midway between the hilum and the margin, and also 

 those near the hilum. The lamellaj average about 10 to the larger gi-ains. 



The grains vary in size from 5 to 25/i. The conamon size is 14yu. 



Polariscopic Properties. The figure is centric, or slightly eccentric, and distinct, and is in the 

 form of a very distinct cross. At the base another figure may be frequently seen which appears on 

 the chstal side of a depression of a facet. The lines of the cross are clear, straight, and of equal dis- 

 tinctness throughout, except towards the margin, where they are broader and less well defined. 



The degree of polarization is high. It varies in different grains, but not very much in different 

 aspects of the same grain, except at the base, where it is less marked. 



With selenite the quadrants are sharply defined, regular in shape, but unequal in size, 

 colors are pure. 



Curve of Reaction-Intensities of Starch of Cycas revoluta. 



The 



