56 BOTANY 



by the pond. When this has happened we see that 

 the one community of plants, viz., the woodland, has 

 ousted the other, the community of water plants. It 

 is not only individuals that struggle against each other, 

 but whole communities that usurp each other's place. 

 Here, indeed, we can hardly say that there is a struggle 

 between the land and the water plants and those of 

 the shallow shore, because by their natural growth and 

 accumulation the former merely follow on where the 

 latter have, by their own growth, rendered the place 

 no longer suitable for themselves, but well adapted for 

 those which need a built-up soil. 



Recently it has been recognised that there are definite 

 laws which govern the series of communities that 

 inhabit a region, and a trained ecologist, seeing one set 

 of plants growing under certain conditions, can predict 

 accurately what type of community will follow it 

 always supposing that there is no great physical change, 

 such as would be caused by the sweeping away of the 

 land by a great flood or its disturbance by a landslide. 



When such a case as this occurs, and we have bare 

 fresh land exposed, it is of interest to watch the way 

 it is colonised. The general law that is followed is a 

 series of changes, first from an entirely bare space to 

 one with a few species scattered at fairly regular wide 

 intervals over the surface, then by more species, the 

 individuals growing closer together, but each still with 

 space to develop completely. At this stage there are 

 generally a very considerable number of species in 

 proportion to the actual number of individuals. Then 

 the species really adapted to the soil and the conditions 

 begin to take a firm hold, and they grow more crowded 

 together and oust the others, till at the end, when the 

 vegetation for the spot is firmly established, there are 



