296 .NATURE OF BOG MOSSES 



of the country are carpeted with them. The mosses are leafy 

 stemmed plants like the Jungermaniales, but they usually 

 possess the decided advantage of having erect stems and radi- 

 ally arranged leaves (Fig. 200). Even in the prostrate forms 

 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. 



1 08. Order a. Sphagnales. Bog or Peat Mosses. A single 

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

 representative of this order and in several respects it occupies 

 an intermediate position between the hepatics and the mosses 

 proper. These pale-green mosses (Fig. 201) grow on bogs and 

 moors and other places where they are subject to drainage con- 

 taining 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, orchids, pitcher plants (Sar- 

 racenia) 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 insectivorous plants, and of certain trees and 

 shrubs that are associated with mycorrhiza. The sphagnums 

 grow luxuriantly in such places, the lower portions of the stem 



