(n6) 



and their accumulation forms peat. The "black mosses" 

 {Andreaea) differ from both of the other groups in the 

 valvular capsule; they grow on dry rocks. The true mosses 

 vary exceedingly in size and aspect. An examination of 

 the specimens in the exhibition cases will convey to the 

 mind a better idea of this group than may be gained from 

 a description. They grow under all kinds of conditions 

 from dry rocks to deep water. Many of the kinds grow on 

 almost any kind of rock, earth, or bark of trees, while 

 certain ones are more particular as to their habitat. Some 

 will thrive only on limestone, which they often gradually 

 disintegrate and partially preserve in the masses of closely 

 set plants as a calcareous tufa; other species prefer ground 

 that has recently been burnt over, as species of Funaria 

 and Leptobryum, while others grow only on the bones of dead 

 animals or in places where animal refuse has accumulated. 



Next higher in the plant kingdom is the subkingdom 

 Pteridophyta, or ferns and fern-allies, the seedless plants 

 with roots, stems, leaves, and woody tissue (cases 51 to 

 55). The ferns as a group perhaps attract the attention 

 of a greater number of people than any other series of 

 plants. Associated with what are usually known as ferns 

 are the fern-allies, for example the "horse-tails" (Equi- 

 setum), "lycopods" (Lycopodium), and "quillworts" (Iso- 

 etes), but these are usually less conspicuous than the 

 "ferns." Fern-plants differ from all the plants of simpler 

 organization in having vascular (woody) tissue, that is, 

 a system of vessels for conducting sap through the different 

 parts of the plant-body. They exhibit an almost infinite 

 variety of form; their stems may be underground, hori- 

 zontal on the ground, or erect; the leaves are either simple 

 or compound, and sometimes perform both the work of 

 foliage leaves and that of bearing the spore-cases (ferns), 

 while in other cases some of the leaves have become changed 

 into mere spore-bearing organs (cinnamon-fern). 



The "flowering" plants (cases 56 to 128) comprise a 

 single subkingdom, the Spermatophyta, or seed-bearing 



