16 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS 



Roots, stems, and leaves taken together constitute the vegeta- 

 tive organs of the plant body, or the apparatus by which it 

 carries on the processes necessary for its life and growth. 

 In a general way it may be said that the roots serve to anchor 

 the plant and to absorb water and dissolved raw materials 

 from the soil to aid in the manufacture of plant food, that 

 the stem conducts water and plant foods, and that the leaves 

 carry on most of the work of food making for the plant and 

 of admitting oxygen for respiration. 

 E. The flower. Note the occurrence of flowers at intervals along 

 the stem. Locate the points from which flowers may arise. 

 Sketch a short section of the stem with a flower attached. 

 Make a drawing of a flower (side view), noting the spur which 

 extends for some distance nearly parallel to the flower stalk. 

 Examine the outer surface and the inner surface of the 

 flower to see how the somewhat leaf -like but bright-colored 

 parts which inclose it are related to each other. The five 

 outer portions together make up the calyx, and the five 

 inner ones the corolla. Calyx and corolla together consti- 

 tute the perianth. Cut away the members of the corolla 

 and note in the interior of the flower the eight curved stalks, 

 each surmounted by a knob, and within them a smaller 

 object, split at the tip into three divisions. The knobbed 

 organs are stamens and the innermost organ is a pistil. 

 E. The fruit. Eind a series of old flowers in which the calyx 

 and corolla have become more and more withered, and trace 

 the development of the lower part of the pistil into a green 

 three-lobed fruit. Cut across a large, nearly dry fruit and find 

 out how many seeds are contained in each of its divisions. 

 2. Reproduction in the seed plant. Stamens and pistils taken 

 together constitute the reproductive organs of the plant. The 

 calyx and corolla aid the work of the stamens and pistils in 

 various mechanical and other ways.^ The use of the flower is to 

 bear seed, and seed formation is brought about by the action 

 1 See Principles, Chapter XXXII. 



