14 



VEGETABLE PHYSIOLOGY. 



LESSON 4. 



78. This very valuable product constitutes an important ele- 

 ment of all the cereal (edible, as wheat, etc.) grains ; it forms the 

 nutritive principle of the leguminous plants (Peas, Beans], and is 

 more or less actively distributed throughout the vegetable kingdom. 

 It occurs in every plant, and it is found in every part ; it will only 

 pay the cost of separation, however, when found in the root, tubers, 

 seeds, fruits, and (more easily, as in the Sago Palm) the pith. 



FIG. 17. 

 FIG. 16. 



Corpuscle of Potato Starch, 

 magnified. 



FIG. 18. 



Section of Potato, showing 

 the starch in situ. 



Corpuscle of Tous les mois, 

 magnified. 



79. The Potato (Fig. 16) is found to consist of cells of variable 

 size, formed of cellulose, and filled with corpuscles of starch these, 

 too, vary remarkably, some being very large, others minute, and the 

 remainder of intermediate size, so that every cell may be quite full. 



80. Examined by the Microscope, a corpuscle of starch (Fig. 17) 

 is a very interesting and beautiful object; each corpuscle possesses 

 somewhere, but its situation is uncertain, a circular spot called the 

 hilum; this is (erroneously) supposed to be its point of attachment 

 to the cell- wall. Around the hilum, a number of extremely delicate, 

 transparent, concentric rings are seen. 



81. The observer will, however, sometimes look for these charac- 

 teristics in vain not a single corpuscle of the veritable tissue is 

 found to display them ! The secret is that the hilum and concentric 

 lines are placed only on one side, and the other side chances to be 

 uppermost. 



82. The largest known corpuscles of starch in the vegetable 

 kingdom are found in Canna cocdnea, or Tous les mois (Fig. 18), a 

 plant extensively cultivated in the South of France; the peculiar 

 French name signifies " every month," and is given to the plant from 

 the circumstance of its flowering monthly ; here the hilum and con- 

 centric lines are distinctly seen. 



