136 GENERAL BOTANY 



perpetuation of the life of the species is concerned. The plant body, 

 being of importance for the warm season only, can consequently be 

 delicate and small, so that the entire energy of the organism may 

 be concentrated on the reproductive structures. Annuals, on the 

 other hand, are not able to hold their ground against such perennials 

 as dandelions and grass, since these plants retain a position once 

 gained and spread out vegetatively from year to year. Annuals 

 are therefore good immigrant plants, which find new places and 

 occupy them temporarily. They are able to do this by means of their 

 seeds, which are produced abundantly each year and are readily 

 disseminated by wind, water, and animals ; but in the end they 

 are usually crowded out of their places by the hardier and longer- 

 lived perennial plants. Biennials have an advantage in special- 

 izing the first season on the production and storage of a large 

 amount of food and in devoting this food storage during the second 

 season to the maturing of fruits and seeds. The biennial habit is 

 especially adapted to regions with recurring dry and wet seasons. 

 In such localities the rainy season, which is usually short, is suffi- 

 cient for the production of a new plant body and the storage of a rich 

 food supply. During the dry season such plants lose their leaves and 

 hibernate in the form of underground rhizomes, bulbs, or tubers. Dur- 

 ing the second rainy season flowers, fruit, and seeds are produced, by 

 means of which the species is preserved and disseminated. Herba- 

 ceous perennials are also adapted to such climatic changes as those 

 indicated above, and have the additional advantage of the perennial 

 habit. In the temperate regions of the United States, perennials 

 also represent the dominant herbaceous types, since they easily adapt 

 themselves to medium, dry, and wet situations and hold the territory 

 once gained from the less enduring annuals. 



Trees and shrubs, although adapted to endure great variations in 

 the environment, are not the equals of the herbaceous perennial 

 grasses and allied plants in adapting themselves to wide ranges of 

 climate and soil. This is shown by the fact that the great deserts, the 

 plains, and the high mountain areas are not their usual habitats. 

 The prophecy has therefore been made that the future vegetation of 

 the earth will be derived from the herbaceous perennial type of 

 plants. The tree type had its origin in the remote past, as our coal 

 deposits testify. It may have given rise to the herbaceous per- 

 ennials of to-day, and it may succumb in the future to the younger 

 and more progressive herbaceous perennial and its offspring. 



