STABCH, AMYLOID. 55 



original nucleus. The layers are commonly much thicker on one 

 side than the other, so that the dot or nucleus, which all the lines 

 surround, becomes very eccentric. Starch-grains lie loose in the 

 cell 'where they are formed, and are usually separate and simple. 

 But occasionally two or more small grains are combined by new 

 layers into one, and in some plants they are regularly united into a 

 cluster or compound grain, as in West-India Ai-rowroot, the corms 

 of Colcliicum and Ai-um, and the rootstocks of the Water-Lily 

 (Nymphtea) and Water-Shield (Brasenia). In the latter the grains 

 are oblong or club-shaped, and remarkably large. Starch-grains are 

 nearly uniform in the same plant or organ, and of very different 

 appearance in different plants : so that the smallest quantity of 

 starch from the potato, wheat, rice, maize, arrow-root, &c., may at 

 once be distinguished under the microscope. In this way adultera- 

 tions of arrow-root, &c. may be detected. The outer layers of 

 large and well-developed starch-grains (such as those of the potato) 

 are denser than the inner : consequently, each grain is marked by a 

 diu-k cross when viewed by polarized Hght. Starch is unaffected 

 by cold water ; but hot water is absorbed by it ; the inner part of 

 the grain softens first and swells, inflating the denser superficial 

 portion into a large sac, which may at length burst or be dissolved. 

 It thus forms a jelly with boihng water, but is not really soluble in 

 it. When truly dissolved, it is no longer starch, but, by a slight 

 change in its character, it is changed into dextrine (80). Tlie 

 chemical test of starch is iodine, which turns it blue. 



82. Starch is the form in which nourishing matter is stored up in 

 the plant for future use ; in which respect it may be likened to the 

 fat of animals. It is the ready -prepared material of vegetable fabric, 

 — the same as cellulose in a particular and more soluble form, — 

 accumulated in the cells of certain parts as a provision for future 

 growth. When about to be used, the grains are dissolved in the 

 plant at the natural temperature ; that is, the starch is converted into 

 dextrine, which differs chiefly in being soluble in cold water, and this 



' changes into sugar, which is still more soluble ; and thus a sirup is 

 formed, which the sap dilutes and conveys to the adjacent parts, or 

 to Avherever growth is going on. 



83. Amyloid (of which Bassorin, Salep, and Pectine are apparently 

 modifications), which in solution is J^egefable Jelly, is intermediate in 

 character between starch, dextrine, and cellulose, and has nearly the 

 properties of starch, when this has been altered by hot water. It 



