422 LIFE ON THE EARTH 



anchors the plant to the ground and takes in from the soil 

 all the plant's food except carbon. This is supplied from 

 the, carbon dioxide of the air, which enters the plant through 

 the leaves. Leaves are the original food manufactories for 

 all plants and animals. Stems vary greatly in the positions 

 they assume, but their chief functions are to support the 

 leaves and to conduct food solutions from the root to the 

 upper-structure of the plant. The two great classes of 

 stems are monocotyledonous and dicotyledonous. 



The stem also usually supports the flower, which consists 

 in the main of calyx, corolla, stamen, and pistils. The chief 

 function of the flower is to produce the seeds from which 

 succeeding generations of plants grow. The enlarged tip of 

 the stamen is called the anther. This produces pollen 

 grains. When a pollen grain of the right sort falls on the 

 head of the pistil, called the stigma, it fertilizes an egg cell 

 in the ovary, which is at the base of the pistil, thus produc- 

 ing the embryo of a new plant, which is the living part of a 

 seed. Pollen grains are carried and spread by the wind and 

 by insects and birds. The seeds are also scattered by the 

 wind, by animals, and by flowing streams. 



Besides these green plants which prepare their own foods, 

 there is another great group of plants that may be called 

 dependent. Instead of preparing their own food by the 

 help of the sun, they live upon food that has been prepared 

 by green plants. 



Among the familiar dependent plants are mushrooms and 

 toadstools. Bacteria and yeasts are single-celled dependent 

 plants. A bacterium reproduces by dividing in two. A 

 yeast reproduces by budding. Molds are dependent plants 

 which are\made up of many cells and which reproduce by 

 spores. 



