CHAPTER XXI 



MONOCOTYLEDONS 



Habitat and habit. The monocotyledons include over forty 

 known families and about twenty-five thousand species of plants, 

 the greater number of which are water-loving, being either true 

 hydrophytes, like the pondweeds (Pontederia and Potamogetori), 

 or semiaquatics, like the marsh grasses and sedges. A few forms, 

 such as the yuccas and desert grasses, are xerophytic, while a 

 large number should be classed as tropophytes, adapted to alter- 

 nating seasons of moisture and drought. Among these plants are 

 many of the wild and cultivated species in which the underground 

 stem takes the form of a rhizome, bulb, or corm, which enables 

 the plant to live securely underground during an inclement 

 season. The favorable season with such plants is used for the 

 growth of aerial stems bearing leaves which make food, and for 

 the production of flowers, fruit, and seeds. The majority of these 

 species have the characters already ascribed to monocotyledons, 

 namely, narrow, parallel-veined leaves, aerial stems with scattered 

 bundles, and flowers on the plan of threes. 



Reproduction and seasonal life. The monocotyledons with 

 underground stems reproduce sexually by means of flowers and 

 vegetatively by means of corms, bulbs, runners, or tubers formed 

 as offshoots from the mother plants. Vegetative reproduction 

 facilitates local increase in the immediate vicinity of the mother 

 plant, while seeds, formed as a result of sexual reproduction, 

 facilitate the distribution of the species over wide areas. The 

 seasonal life is therefore much the same as that of the white 

 sweet clover and of the perennials outlined in the summary of 

 the seasonal life of plants in Part I. 



The commercial importance of the monocotyledons is due to 

 the great beauty of many species, such as the lilies, tulips, and 

 hyacinths, and to the value of other species for food and forage. 



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