DEVELOPMENT OF PLANTS 2>77 



swing back and forth in the wind. The two lobes of the anther 

 now curve apart and open at their ends by a narrow slit, forming 

 a cup in which the microspores collect (Fig. 283, 5). As the 

 rocking of the anther in the wind sifts out the spores, more 

 rattle down into the cup and so a very gradual scattering of the 

 spores is effected. This entire process may be effected in a few 

 minutes, and in the case of the wheat each flower is said to last 

 for only 15 minutes. The Graminales includes two families: 

 The Graminaceae, or grass family, and the Cyperaceae or sedge 

 family. The grass family is by far the more important and is 

 distinguished by the usually hollow aerial stems, two rows of 

 leaves with sheathing bases split and the fruit is generally a 

 grain (Fig. 284, 6). The sedges are largely paludose and of 

 little value, the stems and leaves being often silicified. They 

 usually have solid stems, three rows of leaves with sheathing 

 bases entire, more simple flowers and the fruit is usually an 

 akene (Fig. 285). 



132. Arales, the Aroid Order. — These plants are largely tropi- 

 cal and are characterized by large and generally net-veined leaves 

 and showy inflorescences and fruit (Fig. 286). They present 

 an odd series of striking forms quite different from other mono- 

 cotyledons. Many of them are familiar plants owing to their 

 extensive cultivation in green-houses, as the calla lily (Richardia) , 

 Caladiam, often with variegated leaves, and the gigantic leaves of 

 Dracontium and Colocasia, known as the elephant ear, and the 

 curiously perforated leaves of the Monstera. Many species of 

 Anthitrium are climbers and reach to the top of the highest 

 trees, sending out with great regularity from the successive 

 nodes, naked branches that may reach the ground and form roots. 

 The order is represented in temperate regions by a few very 

 familiar genera as jack-in-the-pulpit (Arisacma) , skunk cabbage 

 (Spathycma), golden club (Orontium), sweet flag (Acorus), 

 water arum (Calla). The duckweeds that float upon every 

 pond are extremely reduced allies of the order, representing the 

 smallest seed plants known, Woltta being an oval, rootless 

 plant scarcely one millimeter in diameter. 



The inflorescence is usually covered, as in Typha, with a bract 



