282 NATURE OF BOG MOSSES 



where but two rows of leaves can be developed, the resemblance 

 to the leafy hepatics is only superficial. The moss leaves are 

 not lobed and the central portion is usually traversed by a strand 

 of cells which serve for conduction like the vascular bundles of 

 higher plants (Fig. 206, B). The differentiation of the tissues 

 of the stem also shows a marked advance over preceding forms. 

 A central conducting region of elongated cells that may be 

 compared to a rudimentary vascular system and a cortical zone, 

 often with thickened cells and rudimentary epidermis, are fre- 

 quently to be seen (Fig. 206, A). Asexual reproduction is al- 

 most entirely confined to the detachment of branches as stated 

 above. In only a few genera have the formation of gemmae been 

 noticed. The sexual reproduction and the development of the 

 sporophyte present some interesting features that will be noticed 

 in the following orders. 



108. Order a. Sphagnales. Bog or Peat Mosses. — A single 

 genus, Sphagnum, of numerous poorly defined species is the sole 

 representative of this order which forms in several respects a 

 transition from the hepatics to the mosses proper. These pale- 

 green mosses (Fig. 201) grow on bogs and moors and other places 

 where they are subject to drainage containing organic matter, as 

 humic acid, derived from the decay of plant and animal life. The 

 majority of plants are unable to endure these conditions, which 

 are popularly referred to as sour, and as a result, you will always 

 find associated with the bog mosses a rather limited and peculiar 

 variety of plants such as several genera of heaths, sedges, or- 

 chids, pitcher plants (Sarracenia) and other insectivorous plants 

 like the sundew (Drosera). For some reason the ordinary 

 plant is not able to procure its food from these sour bogs and 

 this may explain the common occurrence in such places of in- 

 sectivorous plants, and of certain trees and shrubs that are asso- 

 ciated with mycorrhiza. The sphagnums grow luxuriantly in 

 such places, the lower portions of the stem dying off and the 

 upper portion branching and continuing the growth from year 

 to year. In this way, ponds are gradually covered with a layer 

 of mosses which become rather insecurely bound together by 

 the subsequent introduction of other plants whose roots or stems 



