290 A TEXTBOOK OF GENERAL BOTANY 
Starch. Starch is a polysaccharide having the general formula 
(C,H,,O,),. in which n is a large number. Starch is insoluble 
in cold water and occurs in 
plants in the form of grains 
(Figs. 34, 289, 290). Starch 
grains from different plants 
have different shapes and 
configurations. Owing to this 
fact it is possible to identify 
starches by the use of a micro- 
scope. The starch grains are 
found in amyloplastids (Fig. 
Fic. 291. Single grain of potato starch 291). Starch a formed from 
within an amyloplastid (left) and amy- sugar and is easily converted 
loplastid with starch grain removed into sugar, either in plants or 
(right). (x 765) in a chemical laboratory. The 
storage of carbohydrates in 
the form of starch has the advantage that the starch is insolu- 
ble and therefore does not produce excessive osmotic pressure. 
Inulin. Inulin, like starch, 
isa polysaccharide and belongs 
to the general class of starches. 
In some plants, particularly 
the Compositae, inulin occurs 
in considerable quantities. 
Inulin is soluble in water and 
occurs in plants in solution. 
It can be precipitated by alco- 
hol, when it forms characteris- 
tic spherocrystals (Fig. 292). 
Atter being. extracted trom Fic. 292. Spherocrystals of inulin in 
plants it is a white powder cells of dahlia root. (x 304) 
like starch in appearance. 
Hemicellulose. In some seeds food is stored in thickened cell 
walls in the form of hemicellulose, or reserve cellulose. Food 
is stored in this form, however, much more rarely than as sugar 


