30 STARCH GRANULES.—FORMS AND SIZES. ‘ 
Starch is not only widely distributed through, the different 
parts of a plant, but it also occurs ya varying quantity in all. 
classes of plants with the exception of the Fungi. West Indian 
Arrow-root (fig. 46), Sago (fig. 47), Tous-les-mois (fig. 48), and 
Potato starch (fig. 49) may be mentioned as familiar examples 
of starches derived from different plants. In all cases starch is 
a transitory product stored up for future use, resembling in 
this respect the fat of animals. When thus required for the 
nutrition of the plant, it is converted previously, as will be 
afterwards seen, into dextrin and sugar, which are soluble sub- 
stances, and can therefore be at once applied to the purposes of ~ 
nutrition, which is not the case with starch in its unaltered 
condition, as it is then insoluble. 
When fully formed starch is found floating in the cell-sap 
(fig. 45) in the form of colourless granules or grains, which are 
either distinct from one another as is usually the case (figs. 46 
and 47), or more or less combined so as to form compound 
granules (fig. 50), as described on page 38. 
Fie. 45. Fic. 47. 
Fig. 45, Cell of the Potato containing starch granules.——Fig. 46. West- 
India Arrowroot ( x 250).——Fig, 47. Sago meal (x 250). 
In form the separate granules are always spherical or nearly 
so in their earliest condition. In some cases this form is nearly 
maintained in their mature state, as in Wheat starch (fig. 51) 
but the granules frequently assume other forms, as ovate, 
elliptical, more or less irregular, club-shaped, or angular (figs. 
46-49 and 52). Such forms arise from the unequal development 
of the sides of the granules, or from mutual pressure—the same: 
causes, indeed, as we shall see, which give rise in a great measure 
to the varying forms of the cells in which they are contained. 
Starch granules vary also extremely in size in different plants, 
and even in the same cell of any particular plant. The largest 
granules known appear to be those of Canna starch, or, as it is 
commonly termed, ‘ Tous-les-mois,’ where they are sometimes 
as much as the 555 of an inch in length (fig. 48); while the 
smallest granules, among which may be mentioned those of Rice 
starch (jy. 52), are frequently under 4; of an inch in length. 
