WD ester ICV & 
aie } SR oe ! ; ,4 it ry eter oi Jo ; ; ‘ , ¥ 
VANA > : ‘4 I rl f “ 4 / : . ij 
5 ee x J yar De id r By} por 
i | 
rg he Cell as an Individual. 27 
a 
~ 
- colour on treating with an aqueous solution of iodine.' They have the, 
same chemical composition as cellulose, C,H,,O; ; they are insoluble in 
cold water, but swell up very strongly in boiling water, forming a 
paste. Ifstarch mixed with saliva is heated for some time to 45° or 
- 55° C., the substance which is coloured blue by iodine is removed. The 
that is coloured blue by iodine, granzdiose, together with a cellulose 
conclusion which naturally follows, that starch consists of the substance 
substance that is not so coloured, called farzzose, must not, however, be 
considered as finally determined. The grains of starch are always 
Fic. 43. — Starch- Fic. 44.—a, 4, starch- Fic. 45.—Starch-grain from 
grain from the scar- grains from rye. (x the stem of the sarsaparula, 
let-runner. (x 660.) 660. ) Smilax Sarsaparilla. (x 
660.) 
formed originally within the chlorophyll. On their first origin they appear 
as infinitesimally small bodies, which are invariably of a spherical form 
until they have attained a certain size. In the course of their further | 
growth they deviate in a variety of ways from this form (Figs. 42-46). 
The fully-developed starch-grains of the sorrel and of the tuberous roots 
of the orchis are spherical ; those of the grains of cereals lenticular ; of 
the potato ovoid ; grains of the shape of a rod or bone are found in the 
latex of tropical Euphorbias, &c. (Fig. 46.) ) 
Mature starch-grains consist, as a rule, of a num er of layers which- 
appear to have been deposited around a central or eccentric nucleus ; 
but it is impossible to believe that separate layers have been actually 
so formed in the course of growth; it is much more probable that 
they grow by intussusception (see p. 15), and that the stratification is 
only the consequence of the layers-or shells containing a larger or 
smaller quantity of water, as is shown by perfectly dry grains of starch 
being unstratified throughout. Those grains which contain two or more 
/ 
} An exception. is perhaps afforded by the membranes of the asci of 
Lichens, with respect to which, however, it is at present undetermined 
whether they contain starch or not. 
