1898. 



on a YorJi'shire 3Io 



623 



moors uear Keigliley burst in 1824, and coloured tlio river with a 

 peaty stain as far as to the Humber. In December 1896, a bog of 

 200 acres burst at Rathmore, near Killarney, and ihe eftects were 

 seen ten miles off. Nine persons perished in one cottage. 



The soaking up of water is essential to the growth of the Sphag- 

 num, which employs several different expedients for this purpose. 

 Its slender stems give off numerous leafy branches, and also branches 

 which are reduced to filaments. 

 These last turn downwards aloug 

 the stem, which they may almost 

 C(mceal from view. The crowded 

 leaves have in-folded edges. There 

 are thus formed innumerable narrow 

 chinks, in which water may creep 

 upwards. The microscope brings 

 to light further contrivances, which 

 answer the same purpose. Many of 

 the cells of the leaf lose their living 

 substance, and are transformed into 

 water -holding cavities with thin 

 transj^arent walls, which are pre- 

 vented from collapsing by spirally 

 wound threads. But the water must 

 not only be lodged ; it must ascend, 

 and supply the growing blanches 

 above. Accordingly the water - 

 holding cells are not closed, but 

 pierced by many circulir pores, 

 which allow liquid to pass in and 

 out freely. Perforated water cells 

 also form the outer layers of the 

 stem. Thus the whole surface of 

 the plant, whether immersed or not, 

 is overspread by a water film, which 

 is easily replenished from below as 

 it evaporates above. It is the water 

 spaces which render the Sphiignum 

 so pale. The green living sub- 

 stance forms only a thin net vorh, 

 traversing the water-holding tissue. 



Now and then we are lucky enough to see the bed of a Sphag- 

 num swamp. Quarrying, or a landslip, or the formation of a new 

 watercourse, may expose a clean section. I have known the mere 

 removal of big stones, time after time, from the bed of a stream fed 

 by a Sphagnum swamp, gradually increase the cutting power of the 

 running water, until the swamp is not only drained, but cut clean 

 through down to the solid rock. Then we may see that the peat rests 

 upon a sheet of boulder clay, and this upon the sandstones and shales. 



Fig. 2. — Detail of Spbagnura Uaf ; 

 green cells with corpuscles, ami 

 water-cells with spiral threads 

 and pores. Below is a section 

 (from Sachs) of part of a leaf. 



