2b4 SYSTEMATIC BOTANY 



CHAPTER XXI 

 CLASS II, MONOCOTYLEDONS 



In the second division of Angiosperms, namely Mono- 

 cotyledons, the embryo has only one cotyledon and is 

 generally surrounded by endosperm. The plants are 

 usually herbaceous ; the stem has many scattered and 

 closed vascular bundles (i. e. there is no cambium between 

 the wood and the bast), and secondary thickening is rare. 

 The leaves are usually parallel-veined and linear. The 

 parts of the flower are in threes, often in five whorls with 

 three parts in each whorl. Most Monocotyledons are 

 perennial herbs and many hibernate by means of rhizomes, 

 corms, or bulbs. Many are characteristic of regions exposed 

 to long, dry periods, e. g. steppes, prairies, and semi- 

 desert areas. The linear grass type of leaf is dominant, 

 and plants of this class cover enormous areas, as in the 

 grassy vegetation of temperate regions, which is a charac- 

 teristic feature in the scenery. We are familiar with it 

 in our pastures, meadows, and cornfields ; in grass moors 

 and cotton-grass mosses ; in reed swamps and the marginal 

 vegetation of our ponds, lakes, and rivers. 



Tree-like forms are exceptional, and are chiefly confined 

 to tropical regions, where they form a conspicuous feature 

 in the vegetation ; the most striking examples are the 

 Bamboos, the Dracaenas (e. g. the Dragon Tree), Agaves, 

 Aloes, and Palms. Many of these have a peculiar mode of 

 secondary thickening. 



The orders in this class include many species well known as 

 important food plants, and also many garden favourites, e. g. 

 Gramineae (Grasses, cereals), Liliaceae (Lilies), Amarylli- 

 daceae (Daffodils), Iridaceae (Irises), Orchidaceae (Orchids). 



