380 PLANT STUDIES 



It is the combination of characters which determines a 

 group. 



250. Monocotyledons. — In the Monocotyledons about forty 

 families are recognized, containing numerous genera, and 

 among these genera the twenty thousand species are dis- 

 tributed. It is evident that it will be impossible to con- 

 sider such a vast array of forms, even the families being too 

 numerous to mention. 



Prominent among the families are the aquatic pond- 

 weeds of various kinds, the marshy ground cat-tails, the 

 grasses and sedges, the tropical palms, the aroids, the lilies, 

 and the orchids. Of these, the grasses form one of the 

 largest and one of the most useful groups of plants. It is 

 world-wide in its distribution, and is remarkable in its dis- 

 play of individuals, often growing so densely over large 

 areas as to form a close turf. If the grass-like sedges 

 be associated with them there are about six thousand 

 species, representing nearly one third of the Monocotyle- 

 dons. Here belong the various cereals, sugar-canes, bam- 

 boos, and pasture grasses, all of them immensely useful 

 plants. 



The palms and the aroids each number about one thou- 

 sand species, and are conspicuous members of tropical vege- 

 tation. 



In temperate regions, however, the lilies and their allies 

 stand as the best representatives of Monocotyledons, with 

 their usually conspicuous and well-organized flowers. 



In number of species the orchids form the greatest 

 family among the Monocotyledons, the species being vari- 

 ously estimated from six thousand to ten thousand. In 

 display of individuals, however, the orchids are not to be 

 compared with the grasses, or even with the lilies, for in 

 general they are what are called "rare plants." Orchids 

 are the most highly developed of Monocotyledons, and their 

 brilliant coloration and bizarre forms are associated with 

 marvellous adaptations for insect visitation. 



