794 THE DISTRIBUTION OF SPECIES BY OFFSHOOTS. 



clouds in the evening sky, whose edges are reddened with the rays of the setting 

 sun ; and i£ I am not mistaken, this Lichen has obtained its name on account of this 

 resemblance. 



The chief Liverworts and Mosses which form rings and wreaths when they grow 

 on the flat surfaces of steep rock-faces and on the bark of old tree-trunks, are 

 Frullania dilatata, Radula complanata, Aviblystegium serpens, Anomodon viti- 

 culosus, and Hypnum Halleri. When they first settle they are scarcely noticeable 

 on account of their minuteness, but they spread very rapidly, their firmly adherent 

 stems forking and radiating out in all directions, the whole plant at a little distance 

 now forming a greenish-yellow spot of circular outline. While growth proceeds in 

 this way round the periphery of the Moss-plant, covering the rock or bark like a 

 carpet by the multiplication of its outer forked branches, the older parts near the 

 original place of settlement become dry, disintegrate, and are blown away like dust 

 by the wind, the naked rock or bare bark thus again coming into view. In this 

 way 5, 10, or 20 new Moss-plants are derived from the original one, and stand in a 

 circle round the bare centre. This circle widens from year to year, until at last it is 

 interrupted by gaps, and then 20 or more specimens of the Moss are seen adhering 

 to the substratum arranged in a circle more than a span from the original settling 

 place. 



In order that the ring or wreath arrangement of the ofishoots above described 

 should obtain, it is necessary that the original plant should dry up and decompose, 

 and that the shoots which radiate from it should also die ofif behind in proportion 

 as their growing points travel away from the centre of the settlement, and, finally, 

 that no new ring-forming species should establish itself, or spread on the dead centre 

 for a considerable time. These conditions are only comparatively rarely fulfilled, 

 and this is the reason that ring and wreath formations are relatively so scarce. 



It happens much more frequently that the plant forming the starting-point of a 

 colony, after it has sent out creeping threads of cells, runners, shoots, and the like 

 in all directions, does not itself perish, but remains living and active in the centre of 

 its separated shoots, even sending out new shoots year after year. In the same 

 way the separated shoots repeat the parent-method of growth, i.e. they send out 

 shoots in all directions like the mother-plant, though perhaps less regularly, and 

 thus of necessity some of the young shoots come back to the bare centre and settle 

 down where the mother-plant originally stood. The following phenomenon may 

 also be observed : A plant gives off annually a pair of horizontal shoots on one side 

 only, let us say on the south; their buds in the course of time become independent 

 plants, and each again sends out a few horizontal shoots towards the south. In a 

 few years' time these offshoots give rise to 20-30 plants, which are more or less 

 distant from the starting-point, according to the length of the shoots. In all these 

 cases the offshoots are not arranged in a ring or wreath round an empty centre, but 

 in lines or clusters. 



Like the ring- and wreath-forming colonies, the offshoots, forming lines and 

 clusters, may be underground or aerial. The receptacles of many Fungi emerge in a 



