9 8 THE BOOK OF NATURE STUDY 



the same time the presence of acids and other products of decay- 

 ing vegetable matter in the mud makes it difficult for the roots 

 to absorb water, hence it becomes necessary to limit the rate 

 at which water vapour is given off by the upper parts of the 

 plant. This explanation is not, however, quite satisfactory; 

 the horsetails and other bog and marsh plants offer interesting 

 problems in plant adaptations. 



The Lycopods or Club-Mosses are very different from the true 

 mosses. The Common Club-Moss (Lycopodium clavatum) grows 

 chiefly on high hills and moors. In Hampshire another species 

 (L. inundatum) occurs on low-lying heaths a hundred feet or so 

 above sea level. The stem of the common club-moss runs along 

 the ground, sometimes for a length of several feet, and gives off 

 numerous branches, some of which are stout and prostrate like 

 the main stem, while others grow erect and give off slender shoots 

 ending in club-shaped thickenings or cones. The creeping stems 

 are densely covered with stiff, narrow, curved, and pointed leaves, 

 and give off roots chiefly at the points where branching occurs. 

 The erect cone-bearing branches have fewer leaves, more closely 

 pressed against the stem, but the leaves on the cone itself are 

 larger and overlap each other. 



The cone bears kidney-shaped spore-cases, one within the 

 base of each leaf. The spore-case opens by a cross-slit, to let 

 out the dust-like yellow spores the " lycopodium powder " or 

 " vegetable brimstone," used for coating pills, for fireworks, 

 and stage lightning, etc. 



The common club-moss is well adapted for existence on 

 exposed and bleak hills. Its wiry but pliable stems run along 

 the surface among the other plants which form the moorland 

 carpet heath bedstraw, tormentil, tough grasses, etc. sending 

 a root here and there into the soil, while the closely overlapping 

 leaves curve inwards in dry weather and prevent undue loss 

 of moisture. 



The only other club-moss at all common in Britain is the 

 Fir Club-Moss (L. Selago\ which is confined to hills and moors. 

 It differs greatly in habit from the common club-moss, for the 

 stem branches repeatedly as it rises from the ground, and the 

 plant, which may be eight inches high, thus acquires a tufted 



