ANGIOSPERM^E 187 



tropical growths, especially in the American tropics, 

 where some species of Philodendron and Monstera are 

 among the most conspicuous plants met with. The 

 smallest and simplest of the family are the duckweeds 

 (Lemna), minute floating plants, the smallest of all 

 flowering plants (Fig. 45, D). These are usually con- 

 sidered to be degenerate relations of the more specialized 

 aroids. Some of the latter possess true compound leaves, 

 which are almost unknown elsewhere among the Mono- 

 cotyledons, and in this respect they resemble the ferns 

 and many Dicotyledons. 



Probably remotely connected with the aroids are the 

 Palms, a large order mainly restricted to the tropics, 

 and one of the most striking types of the vegetable 

 kingdom. A few genera, like the palmettoes of the 

 Gulf States and the fan-palms of southern California, 

 extend beyond the tropics, but it is in the hot, moist 

 regions of the tropics that they reach their most perfect 

 development. Most of the palms, as is well known, are 

 unbranched trees, with a crown of gigantic leaves, either 

 pinnate or fan-shaped. The apparently compound leaves 

 of palms are caused by the tearing into strips of an origi- 

 nally simple plaited leaf, such as occurs permanently in 

 a very few species, and is always found in the seedling. 

 The palms have the parts of the flower in threes, as in 

 the higher Monocotyledons, and they may be either 

 perfect or diclinous, i.e. bearing only carpels or stamens. 

 In the latter case both sorts of flowers may be upon the 

 same plant, or upon different individuals as in the 

 common date-palm. Just what relation the palms bear 

 to the aroids is doubtful, but there is a peculiar group 

 of plants, the Cyclantherse, natives of the American 



