Ch. XIII] THE MONOCOTYLEDONS 529 



tions of marshes, swamps, etc., which were formerly far more 

 prominent and prevalent than now. In any case their 

 evolution has long been independent of that of the Dicoty- 

 ledons despite the remarkable parallelism they exhibit with 

 that group in their floral characteristics. 



When we attempt to subdivide the large groups of Mono- 

 cotyledons and Dicotyledons, we find that both present a 

 series of orders progressively ascending from obviously 

 primitive through well differentiated to highly specialized, 

 without any marked breaks between them. This feature 

 shows chiefly in the flowers, for the vegetative parts and 

 the tissues already possess such high functional efficiency 

 in even the lowest kinds as to leave apparently no room for 

 adaptational improvement, while the conditions of their 

 life, especially competition for space, light, etc., forbid any 

 such fantastic specialization of vegetative parts as the flowers 

 seem free to exhibit. Accordingly we divide the Monocoty- 

 ledons somewhat arbitrarily into three series, as follows : — 



Series A. The Primitive Monocotyledons. 

 Series B. The Differentiated Monocotyledons. 

 Series C. The Specialized Monocotyledons. 



Series A. The Primitive Monocotyledons. 



These have very simple and inconspicuous flowers, either 

 without perianth, or with parts indefinite in number and 

 spirally arranged ; but they are massed into usually bisexual 

 clusters, with commonly a large bract or spathe to each clus- 

 ter. They are largely pollinated and disseminated by wind, 

 though animals are utilized by the higher kinds. They in- 

 clude some four principal orders. 



Order 1. Pandanales: Screw Pines and Cat-tails. 

 About 100 species of shrubs and herbs best known in the 

 Pandanus, or Screw Pines. These are shrubs of tropical 

 regions, cultivated in greenhouses (Fig. 177), dioecious, with 

 spikes of very simple naked flowers, spiral ranks of sword- 

 2m 



