424 Mr. Alfred Russel Wallace [Jan. 22, 



quarter of a million species. The following table, showing how much 

 more crowded are the species in small than in large areas, was exhi- 

 bited on the wall. It affords an excellent illustration of the fact of 

 the great intermingling of species, so that large numbers are able to 

 live in close contact with other, usually very distinct, species. 



Numlers of Flowering Plants* 



The County of Siirrey 

 A portion containing 



The above figures were given by the late Mr. H. C. Watson, one 

 of our most eminent British botanists, and as he lived most of his life 

 in the county, they are probably the results of his personal observation, 

 and are therefore quite trustworthy. 



Continuing the above enquiry to still smaller areas, one perch 

 equalling y^ acre, or less than the yoo^o o ^^ ^ square mile, has been 

 found to have about 40 distinct species, while on a patch 4 ft. by 

 3 ft. in Kent (or about 05 0^0 000 ^^ ^ square mile) Mr. Darwin found 

 20 species. 



The same law of increase of numbers in proportion to areas appUes 

 to the animal world, if we count all the species that visit a garden or 

 field during the year, though those that can continuously live there 

 are not perhaps so numerous in very small areas. 



The Increase of Plants and Animals. 



The powers of increase of plants and animals were next discussed, 

 and were shown to be enormously great. An oak tree may produce 

 some millions of acorns in a good year, but only one of these be- 

 comes a tree in several hundred years, to replace the parent. Kerner 

 states that a common weed, Sisymlirium Sophia, produces about three- 

 quarters of a million of seeds : and if all these grew and multiplied for 

 three years, the plants produced would cover the whole land surface 

 of the globe. 



Equally striking is the possible increase in the animal world. 

 Darwin calculated that the slowest breeding of all animals, the 

 elephant, would in 750 years, from a single pair produce nineteen 

 millions. Rabbits, which have several litters a year would produce a 

 milMon from a single pair in fom- or five years, as they have probably 

 done in Austraha, where they have become a national calamity. As 

 illustrative of this part of the subject, the lecturer referred at some 



* Other tables illustrating similar facts in other parts of the world were 

 prepared, but not exhibited, as being likely to distract attention from the 

 lecture itself. 



