THE VEGETABLE CELL 297 



at once applied to the purposes of nutrition, wliioli 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, it 

 is in the form of colourless granules or grains {Jig. 643), which 

 are either distinct from one another, or more or less combined 

 so as to form compoiuid granules {figs. 649 and 652). 



In form the separate granules are always spherical or nearly 

 so in their earliest condition. In some cases this shape is nearly 

 maintained in'their mature state, as in Wheat starch {fig. 650), 

 but the granules frequently assume other forms, becoming ovate, 

 elliptical, more or less irregular, club-shaped, or angular {figs. 

 644-647 and 651). 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 



Fig. 649. Fig. (ioO. Fig. 651. 



l''i(j. 649. Compound stareli granules of West-India Arrowroot. Aiter Schlei- 

 deu. Wjr. 650. Wheat starch ( x 250). Fig. 651. Eice starch (x 250). 



sometimes as much as the ^J .j of an inch in length {fig. 647) ; 

 while the smallest granules, among which may be mentioned 

 those of Eice starch {fig. 651), are frequently under stmjtt of ^^ 

 inch in length. 



Development of Starch, — Starch first makes its appearance 

 as minute colourless granules in the interior of the chlorophyll 

 grains when exposed to sunlight. These primary starch granules 

 rarely grow to any considerable size. In the parts of the plant 

 which are not exposed to light, grains of larger dimensions and 

 of some complexity of structure are met with. These are formed 

 by the activity of another form of plastid, much like the chloro- 

 plast, but, on account of the absence of the green colour, known 

 as a leucoplast or amyloplast {fig. 646). In a grain formed by 

 such a leucoplast {figs. 647 and 648), we may observe a roundish 

 dark spot, which is termed the hiliim, situated near one end of 

 the granule ; and surrounding this a variable number of faint 



