CLASSIFICATION OF THE MONOCOTYLEDONS. 159 



Probably to be regarded as reduced aroids are the duck- 

 weeds (Lemnacece) (Fig. 86, F, H\ minute floating plants 

 without any differentiation of the plant body into stem and 

 leaves. They are globular or discoid masses of cells, most of 

 them having roots ; but one genus ( Wolffia) has no roots nor 

 any trace of fibre-vascular bundles. The flowers are reduced 

 to a single stamen or carpel (Figs. E, G, H). 



The cat-tail (Typha) and bur-reed (Sparganium) (Fig. 86, 

 7, L) are common representatives of the family Typhcicece, 

 and the pond-weeds (Naias and Potomogeton) are common ex- 

 amples of the family Naiadece. These are aquatic plants, 

 completely submerged (Naias), or sometimes partially floating 

 (Potomogeton). The latter genus includes a number of species 

 with leaves varying from linear (very narrow and pointed) to 

 broadly oval, and are everywhere common in slow streams. 



The largest members of the group are the screw-pines (Pan- 

 danew) and the palms (Palmce). These are represented in the 

 United States by only a few species of the latter family, con- 

 fined to the southern and southwestern portions. The palmet- 

 toes (Sabal and Chamcerops) are the best known. 



Both the palms and screw-pines are often cultivated for 

 ornament, and as is well known, in the warmer parts of the 

 world the palms are among the most valuable of all plants. 

 The date palm (Phoenix dactylifera) and the cocoanut (Cocos 

 nucifera) are the best known. The apparently compound 

 ("pinnate" or feather-shaped) leaves of many palms are not 

 strictly compound ; that is, they do not arise from the branching 

 of an originally single leaf, but are really broad, undivided 

 leaves, which are closely folded like a fan in the bud, and tear 

 apart along the folds as the leaf opens. 



Although these plants reach such a great size, an examina- 

 tion of the stem shows that it is built on much the same plan 

 as that of the other monocotyledons ; that is, the stem is com- 

 posed of a mass of soft, ground tissue through which run many 

 small isolated, fibro-vascular bundles. A good idea of this 



