152 SYSTEMATIC BOTANY. 



bundles. Stomates, like those of higher plants, occur only 

 in the capsules, or sporangia. Most of the Mosses are 

 aerial plants, growing on moist earth or rocks, upon the 

 bark of trees, or occasionally in water ; they are all chlo- 

 rophyll-bearing, and usually of a light-green color. They 

 sometimes multiply non-sexually, as in the Liverworts, by 

 the production of gemmae. These may be produced on the 

 end of the stem ; and when they fall off give rise to a 

 kind of protonema, upon which buds arise, and develop 

 into the leafy plants. At times a protonema is formed 

 from the leaves or root-hairs, and new plants then, in the 

 ordinary way, are formed. The Peat Mosses {Sphagnum) 

 are large, soft, and pale-colored plants, which grow in 

 bogs and swampy places. The leaves are formed of two 

 kinds of tissue, namely, of small cells, which contain chlo- 

 rophyll ; and of large perforated cells, destitute of chlo- 

 rophyll, and containing water. By means of the latter, 

 the plants are capable of taking up and retaining moist- 

 ure, like a sponge. They are, therefore, useful material 

 for " packing" in the transportation of living plants. 

 Twenty or more species of Sphagnum occur in the 

 United States. The true Mosses (Order, Bryacece) pre- 

 sent the highest differentiation of tissue in the Bryophyta, 

 and closely approach the Vascular Cryptogams (the next 

 higher group). The genera are numerous, and have a 

 wide, geographical distribution. In one sub-order, the spo- 

 rangia, or capsule, is developed at the end of the main 

 axis, and these are called the Acrocarpse (Gr. aJcron, top; 

 karpos, fruit) ; common acrocarpous genera are Bryum, 

 Minum, Polytrichum, etc. In the other sub-order, the 

 fruits, or sporangia, are developed laterally, called, there- 

 fore, Pleurocarpae (Gr. pleuron, side) ; Climacium, Hyp- 

 num, etc., are common pleurocarpous genera. 



