FLOWERING PLANTS INTRODUCTORY 95 



materials requires the assistance of energy, and this is derived 

 from the rays of the sun. The leaf displays its broad flat surface 

 to the sunlight, the blade being usually expanded at right angles 

 to the rays of light. The green colour serves to catch certain 

 rays of light that are required in this important process of food 

 manufacture. The characteristic green colour of vegetation 

 thus indicates a widespread similarity in the mode of feeding 

 of plants. 



Even this very brief outline of the uses of the root, stem, 

 and leaf will show how they co-operate in the nutrition of the 

 individual plant. The manufactured materials may either be 

 at once used for the growth of the plant (at their expense new 

 roots and shoots are developed), or they are carried away from 

 the leaf and stored up for the subsequent use of the plant or 

 its progeny. Many individual plants live and grow for years 

 without bearing flowers or giving rise to new individuals. They 

 require for this only the organs which have been described, the 

 roots, stems, and leaves, and these are often spoken of on account 

 of this relation to the growth of the individual as the vegetative 

 organs, and contrasted with the reproductive organs by means 

 of which new individuals are produced. The similarity in general 

 features of the roots and shoots throughout the Flowering Plants 

 shows that the mode of nutrition is similar. When we meet 

 with modifications affecting the whole plant or particular organs, 

 we have to study them in the light of the altered functions of 

 the organs, or of the more profound change in the nutrition of 

 the plant. 



However long the life of a plant may be, it is limited. Some 

 Flowering Plants live for many years (perennial plants), others 

 live for two seasons and die after they have flowered in the 

 second year (biennial plants), while others are annual plants only, 

 living for a single season. Like all other living beings, flowering 

 plants have therefore to provide for the formation and establish- 

 ment of new individuals, i.e. for reproduction. This is always 

 effected by the separation from the parent plant of a larger or 

 smaller part, which is capable of continuing to grow and of 

 becoming an individual like the parent. Sometimes the part 

 which is separated is a bud or a more or less modified shoot, 



