1891.] on British Mosses. 245 



can be answered, and the mind of the beholder is left, as it so often 

 is, when contemplating the richness of Nature, in a state of admira- 

 tion and wonder and ignorance. 



Sphagnacese, — Vast tracts of land in this country and throughout 

 Northern Europe and America are covered with plants of this group, 

 and large tracts which are now fertile agricultural land, where they 

 have entirely ceased to grow, have in former times been occupied by 

 them. The bogs of Ireland, which are mainly constituted of turf 

 moss, were computed in 1819 by the Bog Commissioners to occupy 

 2,830,000 acres. No moss has probably ever, at least in the present 

 state of the globe, played so large a part as the Sphagnum or peat 

 moss. 



Structure. — It is to the peculiar structure of the peat moss that 

 this great part on the theatre of the globe is to be attributed. 



Leaves. — In the young leaves the component cells are all alike ; 

 then by a differential growth we are presented with square cells 

 surrounded by four narrow and oblong ones ; then chlorophyll forms 

 in these narrow cells, but is absent from the square cells ; from these 

 the contents disappear, and water or water-like fluid occupies the 

 whole cell ; subsequently annular and spiral threads develop on the 

 walls of the square cells. The intimate structure of the leaf thus 

 enables it to absorb great quantities of water. 



But again, the shape of the leaves is in many species adapted to 

 the retention of water. By a retardation of the lateral as compared 

 with the mesial growth, the leaf assumes a boat shape. Often the 

 edges of the leaves are turned over ; the leaf thus affords means of 

 holding water. Again, the lateral branches grow in groups from the 

 stem, and some of these branches are generally pendent, and in close 

 proximity to the stem, so that an immense capillary attraction is 

 exerted by them. 



Again, the stem itself is surrounded or rather is more than half 

 occupied by large water-holding cells, and pitchers of a very peculiar 

 form. 



Again, the mode of growth of the plant, abandoning its moorings 

 on the soil and throwing out roots into the water, and growing 

 successively 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 individual thus 

 becoming," it has been said, " in a manner immortal, and supplying 

 a perpetual fund of decomposing vegetable matter."* 



Physical Results from Structure. — The result of these peculiari- 

 ties is that the entire plant of any species of Sphagnum is a perfect 

 sponge. When dry it is capable (as may easily be found by experi- 

 ment) of rapidly absorbing moisture, and carrying it upwards through 

 the plant ; and when growing in vast beds it acts thus on a great 

 scale. Everyone who knows Scotland must know how on many a 



* Macculock, ' Western Islands,' p. 130. 



