144 THE ELEMENTS OF VEGETABLE HISTOLOGY 



materials are always more or less broken, and it may 

 be difficult to secure satisfactory views unless one 

 examines sections. 



The position of the hilum is dependent upon the 

 manner in which the grain is formed by the leucoplast 

 and upon the portion of the grain viewed by the 

 observer. In view of the latter fact one cannot readily 

 determine the position of the hilum in materials 

 examined in temporary mounts until the particles 

 have come to rest. 



The form of the hilum may be modified by the 

 amount of moisture in the grain. Fissures may arise 

 from a point hilum through drying. A stellate hilum 

 shows several radiating fissures. A line hilum is formed 

 by a straight fissure arising from the hilum. A V- 

 shaped hilum results from the formation of two straight 

 fissures from the hilum. 



Striations, when apparent, always encircle the 

 hilum, and are best observed in water mounts. A 

 number of typical starch grains are illustrated in 

 Plate 51. 



Inulin. — This substance occurs in flat tabular 

 masses, in spheroidal masses and in forms closely 

 resembling starch grains. The tabular forms are 

 usually much broken and very irregular (Plate 52, 

 No. 2). Inulin grains or masses do not possess a 

 hilum nor do they show striations. The spheroidal 

 and starch-like forms may show fissures extending 

 from the center of the mass (Plate 52, No. 1). 



Sugars. — The sugars contained in plant cells are 

 usually in solution and are therefore not visible unless 

 the cell liquids become so concentrated that crys- 

 tallization takes place. 



