VEGETATION OF ROCKY PLACES. 605 



for supremacy. The most aggressive species win out in the end. 

 But it must be understood that with this aggressiveness there 

 must also be adaptability to the conditions of environment, for 

 a plant which might succeed under one set of conditions might 

 fail ignominiously under another set of conditions. So, too, 

 certain plants may be especially adapted to a certain set of con- 

 ditions, but may have the effect of so changing the conditions by 

 building up soil or the accumulation of humus that other aggres- 

 sive species may now enter and dispossess them. In this way the 

 plant formations build one upon another, gradually approaching 

 the climax type, which remains permanent so long as conditions 

 are unchanged, but the climax type itself often goes down in the 

 event of the action of great physiographic, climatic, physical 

 changes, or biological factors. 



In the past little attention has been given to the development or evolu- 

 tion of the climax vegetation types from the embryonic ones. Treub, in 

 1888, studied the rehabilitation of plants of the volcano Krakatau three 

 years after the mountain was covered with glowing lava (Bimstein) and 

 volcanic ash. The dry rock and ash was first covered with microscopic 

 blue-green algae (Cyanophyceae), which formed a soil for ferns of which 

 in three years there were eleven species, besides scatte-ed seed -plants. 

 Schimper studied the vegetation of the volcano Gunttir in West Java, which 

 at the time of the eruption in 1843 was covered with glowing volcanic matter. 

 The vegetation was still quite open and in places thin. There were no trees, 

 while shrubs 'and herbs were present as well as numerous ferns, but not 

 forming the chief mass of vegetation as at Krakatau. A remarkable 

 thing was the fact that many species which in the forests were epiphytes, 

 growing near the forest top where they could obtain light, were here grow- 

 ing on the rocks, where in the open formation light was abundant, as 

 many ferns, orchids, and shrubs like Rhodendron javanicum, and Ne- 

 penthes with its pitchers containing water and numerous insects. Flau- 

 hault and Combres have traced the growth of the vegetation in the sandy 

 and dune lowlands of Camargue in the delta of the Rhine, from the naked 

 ground formed in floods, through the open, and later to the close forma- 

 tions (1894). Vegetation established here and there on the beach during 

 the winter is swept by the ocean storms and torn away. But occasionally 

 tufts hold their ground over winter. These increase, catch humus, afford 

 a foothold for other salt-loving plants; a small dune is formed; this grows; 

 the rhizomes of grasses and shrubs binding the soil and holding the life 

 of the plant through the winter period. As the dune becomes larger it 



