180 EVOLUTION OF PLANTS 



Anthurium. This bright-colored "spathe" serves here 

 the purpose of the showy corolla of the higher forms. 



Somewhat higher in the scale are found plants whose 

 flowers are made up of numerous but separate sporo- 

 phylls. These may have carpels and stamens together 

 in the same flower, or they may be separated, as in 

 the common arrow-head (Sagittaria), (Fig. 45, H, J). 

 In these there are also found the accessory leaves, 

 sepals (*) and petals (j?), the latter often large and 

 showy. These forms show certain analogies, both in 

 the structure of the flowers and the tissues, with some 

 of the lower Dicotyledons, especially the buttercup 

 family (Ranunculacese), and it has been suggested that 

 the latter may have been derived from Monocotyledons 

 of this type. 



Of the simplest of the Monocotyledons, the Naiad- 

 acece, or pond-weeds, have been referred to. Other 

 groups which are considered to be very primitive are 

 the Cat-tail rushes (Typhacese), the Bur-reeds (Sparga- 

 macese), the Screw-pines (Pandanacese), as well as 

 several other less-known groups. 



The Aroids (Aracese), of which the common calla lily 

 is perhaps the best-known representative, show many 

 evidences of being a primitive group, especially in the 

 simplicity of the flowers, although there is considerable 

 variety among them in this respect. They are for 

 the most part tropical, although a few genera, Arum, 

 Arisaema, Symplocarpus, and others, are inhabitants of 

 the temperate regions. Some of the tropical aroids are 

 plants of considerable size, the largest being climbers, 

 whose long stems may reach to the top of lofty trees. 

 These climbing aroids are among the most striking of 



