14 TEXTBOOK OF BOTANY 



tapering, underground structures. From observations of tropical plants in 

 conservatories, of mature vines grov^^ing on walls, and of mature corn 

 plants in a field one will learn that roots are not always underground. 

 Stems are still more variable in form. They usually are aerial cylindrical 

 structures, but some also develop below the soil surface and may become 

 greatlv thickened like the tuber of Irish potato. Among the lateral out- 

 growths of stems are the leaves. Only in a few plants will leaves be 

 found originating from other organs. There are myriad forms of leaves, 

 but generally they are flat organs with a very large surface compared 

 with their weight. Those above the surface of the soil are usually green 

 during at least a part of the year. Beginning with such general ideas, one 

 may readilv build more accurate and usable concepts of these organs 

 through further personal observations. 



Flowers are of every size from a twentieth of an inch to thirty inches 

 in diameter, and of every color, often of superb and startling mixtures of 

 colors. Usually flowers are easily recognized, but careful observation is 

 needed to decide what is the flower in the flowering dogwood, Indian 

 paintbrush, calla lilly, jack-in-the-pulpit, snowball, poinsettia, and hy- 

 drangea. Brightly colored parts are not found exclusively in flowers. Nor 

 are flowers always brightly colored, as may be discovered by examining 

 flowers of grasses, sedges, and several kinds of trees. 



Fruits usually develop from the pistils or from the pistils and adjoining 

 parts of flowers. The name fruit is applied to a great variety of structures, 

 such as the dry fruits of the grasses, and "sticktights," as well as the suc- 

 culent berries of the grape and tomato, the fleshy apples and pears, the 

 pumpkins and melons, the firm green fruits of the walnut, and of osage 

 orange. To obtain some notion of the remarkable variety of fruits it is 

 best to observe the transition from flowers to fruits on many kinds of 

 plants at any time such observations can be made in the field or 

 greenhouse. 



Seeds develop from certain structures in the pistil of the flower and are 

 borne inside the fruit. They may be very minute; they rarely exceed a 

 few inches in length. Their most general characteristic is the presence of 

 a firm coat or shell surrounding an embryo plant from which an adult 

 plant may develop more or less like the plant on which the seed was 

 borne. 



Length of vegetative period. The bean plant matures in a few weeks; 

 that is, the formation of reproductive organs takes place after a rela- 

 tively short vegetative period. The vegetative period of plants may be 



