72 THE PLANT WORLD. 



sometimes have a fleshy perianth, and sometimes, as in the quaint 

 " Jack-in-the-pulpit," consist of bare stamens and pistils, the latter 

 occupying the base of the spadix and ripening into a mass of red ber- 

 ries. The leaves of Aroids are of a rich green color, often very large 

 and ornamental, as in the common cultivated Elephant's Ear {Colocasia 

 esculentd) of our lawns. In the Calla Lily {Zantedeschia ^thiopica) 

 the large, pure white spathe and bright yellow spadix very effectively 

 imitate a single flower of some Liliaceous afflnity. When the struc- 

 ture of the spadix is once understood the student will have little diffi- 

 culty in recognizing such plants as the Sweetflag {Acorus Calamus) as 

 belonging to the Araceae, although here the spathe from its position 

 appears to be a mere prolongation of the stem. 



In the Duckweeds, or Lemnacece^ we find the smallest known flow- 

 ering plants. They are supposed to be degenerate Aroids, and consist 

 merely of a little disc-shaped, leaf -like and free-floating body, rarely 

 exceeding one-third of an inch in diameter, and bearing on the under 

 surface a single stamen or pistil and several minute rootlets. There 

 are but three genera and only twenty-five species known throughout 

 the world. In our stagnant pools and ditches Spirodela polyrhiza^ the 

 Large Duckweed, is often abundant, covering the surface with a carpet 

 of green. In another genus, Wolffia^ we see the plant body reduced 

 to a little grain scarcely larger than a pin's head. What a contrast 

 between this and the giant Sequoia ot the Californian forest! 



The Yellow-grass family, {Xyridacecz) will manifest itself chiefly 

 to the one who tramps over a southern pine barren at inidsummer. 

 These plants have slender, grass-like stems, terminated by a dense 

 spike of brownish scales or bracts, from the axils of which appear a 

 few small, evanescent, bright yellow flowers. The structure of the 

 sepals and petals is most beautiful, but very complicated, and can be 

 studied advantageously only by a botanist. The stems are occasion- 

 ally twisted like a corkscrew, whence one of the species is called A'/rw 

 torta. The family contains but two genera, and most of the species 

 are tropical. 



Passing over the inconspicuous Pipe worts {EriocaiilacecE), deni- 

 zens of our fresh water ponds and swamps, with their globose, whitish 

 heads of minute flowers, we come to the Commelinaccu, or Spiderwort 

 family. This contains numerous tropical genera, but none occur in 

 the United States except Commelina and Tradescantia, both of which 

 are cultivated in old gardens. The flowers are a rich, deep blue in 

 most of the species, and they remain open only in the sunshine. In 

 Commelina one of the petals is much smaller than the other two. In 

 this family also we have the flowers subtended and at times partially 

 enveloped by a leafy spathe. 



