BOTANICAL INTRODUCTION. 
257 
class we find the orchis family, the ladies’ slipper, and the 
milkweed. 
19th class. Monoecia. This class Monoecia (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. Dicecia or two houses, has staminate and pistil¬ 
late flowers upon separate plants. This order contains the 
willow or sahx, 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 in 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- 
