10 



BOTANY. 



which have no chlorophyll, or which grow in darkness, do 

 not make starch. 



22. Chemically, starch is much like sugar and cellulose, 

 and like them it is composed of carbon, hydrogen, and 

 oxygen (Cj^HjjOjJ. It contains water in its organization, 



FiQ. 5.— A few cells of the seed of a Pea, showing large starch-grains (S<) and 

 the little granules of aleurone (a). A.t i, i, are shown intercellular spaces. Mag- 

 nified 800 times. 



which may be driven off by heat, or by the application of 



reagents, when it loses its structure. 



23. Starch is a plant-food. It is produced by the green 



protoplasm^ for the nourishment of the plant. As it forms 



only in light, during the day it accumulates, but at night 



by the continued growth of the plant it is mostly used up. 



Whenever there is more made than the plant requires, the 



surplus is stored in certain cells for future use. 



Practical Studies. — (a) Scrape off a little of the substance of the 

 cut surface of a potato tuber. Mount la water and examine under 

 the microscope, using the ^ objective. Note the ovate starch-grains. 



