STABCH-GRAINS. 
57 
cellulose in its reactions ^. At every point of a starch-grain both constituents occur 
together ; if the granulöse is extracted, the farinose remains behind as a skeleton ; 
this skeleton presents the internal organisation of the whole grain, but is less 
dense or poorer in substance, and its weight amounts to only from 2 to 6 p. c. 
of the whole grain. Since the granulöse greatly preponderates and is present at 
every point, the starch-grain shovv's the blue granulose-colouring with iodine 
throughout its whole extent. 
The starch-grains have always rounded forms organised around an internal 
centre of formation ; when young and small the grains appear to be always spherical ; 
but since their growth is scarcely ever uniform, their form changes into ovoid, lenti- 
cular, rounded polyhedral, &c. 
The internal organisation of the starch-grain depends essentially on the dif- 
ferent distribution of water in it [wafer of organisation). Every point of the grain 
contains water in addition to granulöse and farinose. Most usually the amount 
of water increases from without inwards, and attains its maximum at a fixed point 
in the interior. With the increase in the proportion of water, the cohesion and 
density decrease, as also the index of refraction. This change in the proportion of 
water is not, however, constant, but intermittent. To the outermost least watery 
layer succeeds a sharply defined watery layer, to this again a less watery one, and 
so on, until the innermost less watery denser layer surrounds finally a^ very watery 
part, the nucll&ub . All the layers of a grain are disposed round this as their 
common centre, but every layer is not continuously developed round the whole 
in small spherical grains with few layers this is always the case, but 
when their number increases, it does so most in the direction of most vigorous 
growth, which is continuous in a straight or curved line with the direction of least 
vigorous growth. This line is called the axis of the grain, and always passes 
through the nuclei-t s. 
The growth of the grains of starch is accomplished exclusively by Intussus- 
ception ; new particles become intercalated between those already existing both in 
a radial and tangential direction, by which means the proportion of water at 
particular places is at the same time changed. The youngest visible globular 
starch-2:rains consist of denser less watery substance : in this is formed subse- 
quently the central watery ftuolouo ; in the latter a central part may become 
denser; and in this, when the increase in size has advanced sufficiently, a softer 
nucleus may again arise. It may however also happen, after a softer nucleus 
surrounded by a dense layer has arisen by differentiation of the originally dense 
grain, that in the dense layer a new soft one may arise, and it may thus become 
split into two dense layers, the inner of which encloses the soft nucleus. The 
layers increase in thickness and circumference by intercalation. When a layer 
^ [The most recent researches seem to show that the supposed distinction between granulöse 
and farinose is one of mechanical or molecular condition only. The coloration of starch by iodine 
appears not to depend on the formation of a definite chemical compound, but to be the consequence 
of the mechanical interposition of the iodine between the molecules of starch (see Miller's Chemistry, 
3rd ed., vol. III. Sect. 1571, p. 616 s^?.)] 
