202 PRACTICAL LESSONS IN SCIENCE. 



around them with the decaying leaves and stems at length form 

 soil suitable for higher plants. Some species of Sphagnum grow- 

 ing in swamps enter largely into the formation of peat bogs, and 

 perhaps helped to form some varieties of coal. This moss is ex- 

 tensively used in packing trees and plants for shipment, and some 

 species are used for stuffing mattresses. Some species of mosses 

 and lichens are almost the only flora of the polar and high 

 mountain regions. 



Pteridophytes or Ferns, produce no highly colored flowers, yield 

 no rich perfume, yet no group of plants attracts more notice, are 

 more sought for cultivation, or more enjoyed than the ferns, 

 whose sole charm consists in their delicate, graceful, feathery foli- 

 age. Ferns are abundant in all parts of the world, but exist in 

 greatest variety in the hot moist regions of the tropics. There 

 are said to be some 3,000 species ranging in size from less than 

 an inch to the gigantic tree ferns of Australia, some of which 

 reach an elevation of 75 feet, with leaves or fronds which exceed 

 in size those of any other plants. While in general they seem to 

 enjoy rich soil and warm, moist, shady localities, they do grow 

 on exposed hillsides, on rocky cliffs, and sometimes on trees 

 as air plants. They are not only abundant now, but they 

 have been a marked feature in the flora of the earth from very 

 early times. Their remains are found in the rocks of the Devo- 

 nian age, while the coal of the succeeding age is made up mainly 

 of the stems and leaves of ferns and allied plants. 



Ferns consist of a stem, rootstock or rhizoma which is usually 

 horizontal and subterranean, but in some cases it creeps along 

 the surface ; and sometimes it is erect, as in the case of tree ferns. 

 From the rhizoma arises the leaf which consists of a stalk or 

 stipe and the blade or frond. The stipe may be green or black ; 

 may be smooth and polished or covered with scales or hairs; 

 the frond may have an even, uniform outline, like the leaf of an 

 apple tree, or it may be divided and subdivided into many dis- 

 tinct parts, as in the case of the maiden hair fern, so common 

 everywhere. 



The continuation of the stipe through a simple frond is called 



