BOTANICAL INTRODUCTION. 269 



class we find the orchis family, the ladies' slipper, and the 

 milkweed. 



19th class. Moncecia. This class Monoscia (one house), 

 shows to us plants upon the same root, where we find some 

 flowers possessing stamens, others pistils. The stamens are 

 infertile and disappear without fruit, the pistils when fertilized 

 produce fruit. The mulberry-tree, the amaranthus, the genus 

 calla, one species of which gives us the Egyptian lily, a beau- 

 tiful exotic. 



20th class. Dioecia or two houses, has staminate and pistil- 

 late flowers upon separate plants. This order contains the 

 willow or salix, the fig (ficus), mistletoe, so long held sacred by 

 the Druids, and the more useful plants of the hemp and the 

 hop. 



21st class. Cryptogamia. This class includes all plants 

 whose organs of fructification are too minute for our investiga- 

 tion, as mosses, ferns, lichens, and mushrooms. It may be ob- 

 served that many of these plants whose flowers are invisible 

 to the naked eye, present when viewed with a telescope a very 

 curious and beautiful arrangement. It is said that Mungo 

 Park, when once greatly discouraged by the difficulties which 

 environed him on a distant excursion, was so struck with the 

 providence of God, exhibited in the formation of the moss be- 

 neath his feet, that he resolved never to despair, knowing 

 that the same beneficent care would be over all his creatures. 

 In this same class we include the liverworts so useful in medi- 

 cine, the algae or seaweed which swims upon the surface of 

 the water, often covering it to great extent as the fucus nataus, 

 sometimes called the gulf-weed, which is very abundant in the 

 gulf of Florida, and is found m various parts of the ocean, 

 forming masses or floating fields many miles in extent. We 

 must not omit the lichens many of them useful on account of 

 their coloring matter, as letinus which is an excellent chymi- 



