(30 



commonly appendages to aid in scattering the spores, which 

 in this case are not accompanied by spiral threads as they are 

 in the hepatics. The mosses fall into three primary groups : 

 First the "peat-mosses" {Sphagnum) which differ from the 

 rest of the mosses in the development of the tissue-structure 

 of the capsule and the spores; they grow in swamps and 

 other wet places, 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 a descrip- 

 tion. 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 par- 

 tially preserve in the masses of closely set plants as a cal- 

 careous tufa; other species prefer ground that has recently 

 been burnt over, as species oiFunaria 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 Pteri- 

 dophyta, or ferns and fern-allies, the seedless plants with 

 roots, stems, leaves and woody tissue (cases 49 to 55) . The 

 ferns as a group perhaps attract the attention of a greater 

 number of people than any other group of plants. However, 

 associated with what are usually known as ferns are the fern- 

 allies, for example the "horse-tails" (Equisetum), " lyco- 

 pods" (Lycopodium) and " quillworts " (Isoetes) , 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 con- 

 ducting sap through the different parts of the plant-body. 

 They exhibit an almost infinite variety of form; their stems 

 may be underground, horizontal on the ground, or erect; the 

 leaves are either simple or compound, and sometimes perform 



