496 STRUCTURE AND LIFE HISTORIES 



No species of palm has ever been found in both the 

 eastern and western hemisphere, except when introduced 

 artificially. Many of the palms have great commercial 

 value, such as the date palm, cocoanut palm (Fig. 383), 

 fan palm, vegetable-ivory palm (whose endosperm is 

 hard and white like ivory) , and the oil palm. In the trop- 

 ics the leaves of various species are used to make thatched 



FIG. 380. Johnson-grass (Sorghum halpense). Spikelets in a panicle. 

 (After Britton and Brown.) 



roofs, and the trunks are often used for fence posts and 

 porch pillars. 



431. Arum Family (Araceae). The arum family is 

 well illustrated by the "skunk cabbage" (Symplocarpus 

 fcetidus)" (Figs. 384 and 385). 1 The flower has no petals, 

 but four sepals, and four stamens one opposite each 

 sepal. The ovary contains only one suspended ovule. 

 The compound globular fruit is composed of the spongy 

 spadix, greatly enlarged, bearing the coalesced ovaries, 

 with the spherical seeds just underneath the surface. 



1 Called by some authors, Spathyema fcetida. 



