ANGIOSPERMA 187 
tropical growths, especially in the American tropics, 
where sgme 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, ¢.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 Cyclanthere, natives of the American 
