VIII. PLANT GROWTH AND NUTRITION — THE CIR- 

 CULATION AND FINAL USES OF FOOD BY PLANTS 



Problem. — How green plants store and use the food they 

 make. 



(a) What are the organs of circulation ? 



(b) How and where does food circulate ? 



(c) How does the plant assimilate its food ? 



Laboratory Suggestions 



Laboratory exercise. — The structure (cross section) of a woody stem. 

 Demonstration. — To show that food passes downward in the bark. 

 Demonstration. — To show the condition of food passing through the 

 stem. 



Demonstration. — Plants with special digestive organs. 



To the Teacher. — The work following is simply intended to develop the con- 

 cept that the stem is an organ of circulation ; that it puts the upper part of the 

 plant, the food-making organs, in connection with the lower part of the plant, the 

 organs which absorb raw materials for food making and which act as a storage for 

 manufactured food. 



Problem 75 : Groups of plants told by the structure of their 

 stems. 



NOTE. — Plants which produce flowers are divided into two great groups depend- 

 ing on whether they have one or two cotyledons in the seed, i.e., monocotyledons 

 and dicotyledons. A bean is an example of the latter, a corn plant of the former. 

 Certain marked differences in the leaves or stems also appear, the dicotyledon 

 usually has veins forming a network while those of the monocotyledon usually run 

 parallel to each other. A third difference is seen in the stem. In the dicotyledon 

 growth takes place from just under the bark and we have annual rings of growth 

 which tell us approximately the age of the stem. In a monocotyledon (for example 

 a cornstalk) the main bulk of the stalk is made up of pith, while scattered through 

 the pith are numerous stringy, tough structures. These are fibrovascular bundles. 

 The outside of the corn stem is formed of large numbers of these bundles, which, 

 closely packed together, form an outer rind. Thus the woody material gives 

 mechanical support to an otherwise spongy stem. 



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