CELL INCLUSIONS 13 



stained with carotin. Examine also the red cells of a ripe 

 tomato or the yellow cells of a petal of nasturtium (Tropaeo- 

 lum) or the cells of rose hips. 



22. Cell Inclusions. Within many cells are often 

 found bodies not living and not an essential part of the 

 cell but which have been produced by the cell itself. 

 They may be temporary or permanent. They may lie 

 in the cytoplasm, in the vacuoles or in the plastids. 

 Such bodies are called cell inclusions. The most fre- 

 quent cell inclusions are starch, aleuron, crystals and 

 sometimes drops of fat or oil. 



23. Starch. In the green cells of many plants there 

 are produced in the chloroplasts on exposure to light 

 small pearly white grains of starch. 



These are usually transformed into 

 sugar during the night and used by the 

 plant for food or transported to some 

 other part such as root, tuber or seed, 

 where the sugar may be again con- 

 verted to starch, in the leucoplasts, to FlG4 starch 

 remain until needed by the plant for $&&>-* 

 food. Whereas in the green cells of 

 a leaf the starch does not ordinarily accumulate in great 

 quantities, the storage cells of a plant become so packed 

 with it sometimes that little else can be seen. 



Starch is a carbohydrate and is closely related chemi- 

 cally to cellulose and to the sugars. It is composed of 

 carbon, hydrogen and oxygen in the proportions indi- 

 cated by the formula (C 6 Hi O 5 )n, in which "n" is a 

 fairly high but not exactly ascertained amount. By the 

 action of certain organic substances produced by the cell 

 and called enzymes, or of some of the acids and heat, it 

 can be converted into some forms of sugar. 



Starch grains frequently show a concentric structure, 



