42 



KNOWLEDGE. 



[Makch 1, 1892. 



head of the plant form a 

 thick and often widely ex- 

 tended tiift; but lower 

 down the branches grow 

 out laterally from the stem, 

 generally in tufts of four 

 branches, of which, as 

 shown in Fig. 29, two ) 

 generally grow out more ^ 

 or less horizontally, and 

 two are disposed in close 

 proximity to the stem, 

 round which in fact they 

 fall (see again Fig. 16), so 

 as to exert a great capillary 

 attraction and keep a great 

 mass of water in suspen- 

 sion even against the force 

 of gravity. 



Yet further, as it would 

 seem, to add to the absorp- 

 tive capacity of the leaves. 

 Nature, in one or more 

 species of the Peat Moss, 

 has recourse to a further 

 expedient. Bound the base 

 and sides of the leaf, clus- 

 ters of half free cells, with 

 spirally marked walls, are 

 clustered, ready, like their 

 sister cells in the leaf, to 

 carry their full comple- 

 ment of water. Such a 

 group is shown (magnified 

 of course) in Fig. 80. 



The stem of the Sphag- 

 num in like manner is 

 developed as a water- 

 carrying instrument. Its 

 appearance when exaui- 

 ined by the microscope, as shown in Fig. 27 and m 

 Fig. 31, is very singular, for it is surrounded not only 

 with large transparent cells of more ordmary shape, 

 but with large cells developed into the shape ot flasks, 

 with openmgs at then- tops. Fig. 32 will enable the reader 

 further to reaUze this structure. It is a highly-magnifaed 

 section of a quarter of a stem. 



A<^ain, the mode of growth of the plant, abandonmg its 

 moot-ings on the soil and throwing out roots mto the water, 

 and growing suc- 

 cessively year after 

 year, enables it not 

 only to attain great 

 growth, but also, 

 when the occasion 

 demands, to keep 

 pace with the rise 

 of the water in 

 which it may be 

 growing, " the in- .-, ■ 



dividual thus becoming," it has been said, '' m a manner 

 immortal, and supplying a perpetual fund ot decomposmg 



""^fT^limT^lsuits from StrmUur.-The result of these 

 peculiarities is that the entire plant of any species oi 

 Sphagnum is a perfect sponge. ^Yhen dry it is capable (as 

 may easily be foimd by experiment) of rapidly absorbing 

 moisture, and carrying it upwards through the plant ; and 

 when -rowing in vast beds it acts thus on a great scale. 



FlG.29. — Lateral brancliesof Sphaff- 

 niim ; s s, stem ; h h, liorizoutal 

 brandies ; pp, pendant branches. 

 After Seliimper. 



Fi&. .30.— Cluster of cells at base of leaf of 

 Sphagnum acutifolium. -^ter Schimper. 



Everyone who knows Scotland must know how on many 

 a steep moimtain-side, or on the bottom and sides of a 

 corge, these beds will hold up a great body of water agamst 

 the force of gravitv ; and again, the Irish bogs are described 

 as often ascending from the edges towards the interior, 

 sometimes bv a gradual and sometimes by a sudden 

 ascent, so that at times the bog is so high that it reaches 

 the height of the church steeples of the adjoining country, 

 without" any rising ground intervening. 



These peculiarities in the structure 

 of Sphagnum have produced con- 

 siderable physical effects. 



(1) Everyone knows the different 

 effects of rain falling on a land of 

 bare rock or sand, like the Sinaitic 

 desert, and on a porous soil. In the 

 one case it produces a fi-eshet or a 

 flood, that leaves no trace behind ; 

 in the other it is held for a while in 

 suspense, and only gradually passes 

 into the streams. The glaciers and 

 the Sphagnum beds of the mountains 

 of Europe alike act as compensation 

 reservoirs — receive large quantities 

 of moisture as it falls, and retain it 

 till the drier season comes, when 

 part of it gradually passes away •,^ but 

 for these reservoirs, many of the rivers 

 would exhibit a far greater shrinkage 

 in summer and autumn than is now 



tllG CBjSG. 



But (2) the Sphagnum beds have 

 become peat, and have gradually 

 filled up the ancient lakes and 

 morasses, and turned water into dry 

 land.' It is true that peat appears 

 under some circumstances to be formed by other vegetables 

 than Sphagnum, and in all cases it has probably some 

 other plants or roots growing amongst it. ^^i"- ^"-^'^^".if 

 tells us that in Terra del Fuego and the Chonos Archipelago 



peat IS lormeu 

 by two phan- 

 erogamous 

 plants, of 

 which one at 

 least seems en- 

 dowed with an 

 immortality 

 something like 

 that of the 

 Sphagnum ; 

 and the x^eat 

 of the fens of 

 Lincolnshire is 

 formed mainly 

 of Hyimum 

 jluitans. But 

 Sphagnum ap- 

 pears to be the 

 main constitu- 

 ent of peat in 

 Ireland, Scot- 

 land and, so far as my researches have gone, in England ; 

 the pecuhar spiral threads of the cells of the Sphagnum 

 leaf being easily detected in the peat so long as it retains 

 traces of its org'anic origin. 



■Indent i-'.wvs(s.— The Peat Mosses, and the sea-shores 

 of mir islands and of the adjoining mainland reveal, as 

 is very well known, traces of ancient forests. Many parts 



Pia. 31. — Stem of 

 Sphaffuum moUtis- 

 rum, magnified, sliow- 

 ing «H,tlie utricles or 

 flask-shaped cells. 

 After Schimper. 



Fia. 32. — Magnified section of stem of Sphagnum 

 ciimhifoHum. s s^ stem ; «\ x, mass of spirally 

 threaded cells surrounding 

 Schimper. 



.stem. After 



