CELL CONTENTS 143 



Starch. — The transitory or assimilation forms of 

 starch described in Chapter XI are of little importance 

 in food and drug microscopy. Reserve or storage 

 starch grains are fairly constant for a given plant 

 and are of importance in identification work. Starch 

 grains may be classified according to the following 

 characters: 



Number of grains in the mass; 



single or compound. 

 Shape or form of the grains; 



circular, oval and angular forms. 

 Position of the hilum; 



centric or excentric. 

 Shape or form of the hilum; 



point, line and stellate forms. 

 Presence or absence of striations; 



striated and non-striated forms. 

 Size of the grains; 



ranging from 2 to 100 microns. 



The leucoplast produces either single starch grains 

 or masses consisting of several grains. In the latter 

 instance the cluster is termed a compound grain. The 

 shape or form of a starch grain depends upon the num- 

 ber of grains developed from each single leucoplast. 

 The parts of a compound grain are usually angled be- 

 cause of the presence of surrounding grains which exert 

 pressure on all sides. Grains developed in groups 

 of two or three will be flattened on the sides in contact 

 with other grains and rounded on the free surfaces. 

 Beaked forms show a small projection at the hilum 

 end of the grain. 



Starch grains of a given plant range in size within 

 fairly constant limits. In stating the sizes of compound 

 grains, the component parts as well as the whole mass 

 should be considered. Compound grains in powdered 



