Chap. III. 
HIGH HATE OF INCKEASE. 
65 
introduced plants wliich have become common through¬ 
out whole islands in a period of less than ten years. 
Several of the plants, such as the cardoon and a tall 
thistle, now most numerous over the wide plains of La 
Plata, clothing square leagues of surface almost to the 
exclusion of all other plants, have been introduced from 
Europe; and there are plants which now range in India, 
as I hear from Dr. Falconer, from Cape Comorin to 
the Himalaya, which have been imported from America 
since its discovery. In such cases, and endless instances 
could be given, no one supposes that the fertility of 
these animals or plants has been suddenly and tempo¬ 
rarily increased in any sensible degree. The obvious 
explanation is that the conditions of life have been very 
favourable, and that there has consequently been less 
destruction of the old and young, and that nearly all the 
young have been enabled to breed. In such cases the 
geometrical ratio of increase, the result of which never 
fails to be surprising, simply explains the extraordinarily 
rapid increase and wide diffusion of naturalised produc¬ 
tions in their new homes. 
In a state of nature almost every plant produces seed, 
and amongst animals there are very few which do not 
annually pair. Hence we may confidently assert, that 
all plants and animals are tending to increase at a geo¬ 
metrical ratio, that all would most rapidly stock every 
station in which they could any how exist, and that the 
geometrical tendency to increase must be checked by 
destruction at some period of life. Our familiarity with 
the larger domestic animals tends, I think, to mislead 
us: we see no great destruction falling on them, and we 
forget that thousands are annually slaughtered for food, 
and that in a state of nature an equal number would 
have somehow to be disposed of. 
The only difference between organisms which annually 
