TEMPERATE FLORAS 27 



of turf 3 feet by 4, at Down in Kent, Mr. Darwin found 20 

 species of flowering plants growing. 



These facts of the distribution of plants in our own 

 islands prove, that for moderately large areas in the same 

 country possessing considerable diversity of soil and general 

 conditions affecting plant-life, the majority of the species are, 

 as a rule, so widely scattered over it that approximately 

 similar areas produce a nearly equal number of species. 

 Further, we find that areas of successively smaller and 

 smaller sizes have a very much greater number of species 

 relatively than larger ones ; so that, as we have seen, 10 

 square miles may show almost as much variety in its plant- 

 life as an adjacent area of 60 square miles, and that a 

 single square mile may sometimes contain half the number 

 of species found in 700 square miles. 



This characteristic of many small areas being often 

 much richer in proportion to area than larger ones of which 

 they form a part, is a necessary result of the great 

 differences in the areas occupied by the several species and 

 the numbers of the individuals of each ; from those very 

 common ones which occur abundantly over the whole 

 country, to others which, although widespread, are thinly 

 scattered in favourable situations, down to those exceptional 

 rarities which occur in a very few spots or in very small 

 numbers. Those spots or small areas which present the 

 most favourable conditions for plant- life and are also 

 most varied in soil, contour, water-supply, etc., will, when in 

 a state of nature, be occupied by a large proportion of the 

 common and widespread plants, together with so many of 

 the less common or the rare species which find the requisite 

 conditions in some part of its varied soil and aspects, as to 

 produce that crowding together of species and luxuriance of 

 growth which are such a joy to the botanist as well as to the 

 less instructed lover of nature. 



All these peculiarities of vegetation are to be met with 

 in every part of the world, and often in a more marked degree 

 than with us. But this depends very much on diversities of 

 climate and on the extent of land surface on which the entire 

 flora has been developed. The total number of species 

 depends mainly on these two factors, and especially on the 



