18 STARCHES. 



(13) Manihot Starch. 



This variety of search (Fig. 13) is obtained in large quantities 

 from the tubers of Manihot utilissima, Pohl, and other species os 

 Manihot. It is also known under the name of cassava starch, 

 mandioc starch, Brazilian, Bahia, Rio or Para arrowroot, etc. The 

 majority of it is converted into tapioca (see below) before exportation. 



The grains are originally compound, consisting of two, three, or 

 four component grains, and are occasionally found intact. Most of 

 them, however, have been separated into their component grains. 

 They are seldom quite round. Most of them exhibit one or two 

 flat surfaces where other of the constituents of the compound 

 grain have been attached, and are in consequence muller-shaped, 

 cap-shaped, or shortly conical, curved on one side and irregular on 

 the other, etc. ; some are even polygonal. The majority possess 

 a distinct rounded, linear or stellate hilum and delicate concentric 

 striations. The largest measure 25 to 35/x, in length, the smallest 

 5 to 15/j. ; many range from 15 to 25/*. 



(14) Tapioca. 



This substance is prepared from manihot starch, by heating 

 and stirring the moist starch until it agglomerates into the little 

 irregular, rugged masses that are known in commerce as tapioca ; 

 it is usually exported in this form, and constitutes an important 

 article of food. 



The granules of tapioca soften when soaked in water for a few 

 hours, and a small portion, taken preferably from the whiter and 

 more opaque part, can be broken up with the needles in a drop of 

 water and covered with the coverslip, a little pressure being applied 

 if necessary. 



Many of the grains will be seen to have preserved their original 

 shape, and exhibit a distinct hilum ; in many the hilum is stellately 

 fissured ; in others the central part of the grain is a translucent 

 mass, but the outline is still recognisable ; whilst finally many 

 have swollen into a shapeless, unrecognisable mass. These are the 

 various stages in the gelatinisation of the starch by heat in the 

 presence of moisture. 



(15) Starch of Ipomcea Batatas. 



Under the name of Brazilian arrowroot there is also found in 

 commerce the starch of Ipomwa Batatas, Poir. (Fig. 15). The 

 grains are for the most part isolated components of compound grains, 

 but they sometimes occur in groups of two to four. They are very 

 variable in size, the large grains measuring from 25 to 50^, the 

 small from 15 to 22^. They also vary greatly in shape. A few are 

 rounded, some are conical ; others resemble a sugar-loaf cut 

 obliquely, others again are cap or bell-shaped, or even polyhedral. 

 They almost all exhibit a distinct hilum, which is sometimes 

 stellate, sometimes fissured, usually eccentric, and surrounded by 

 striae. 



