Mr. R. B. Hinds on Geographic Botany. 29 



It is not possible to assign a value to species with that preci- 

 sion which can be adopted with families and genera ; any attempt 

 to bestow on them a numerical amount must utterly fail^ making 

 it requisite to adopt some other method. Some idea of their im- 

 portance may be obtained by taking a comparative view of the 

 relations they occupy towards each other, and to the whole mass 

 of vegetation. It would appear that every species of plant has, 

 on an average, somewhere about 281 square miles of surface to 

 increase and multiply on ; and making every allowance for those 

 tracts of country which local causes render unfit to support a 

 vegetation, we become highly sensible how infinitely multiplied 

 the species must be to clothe the earth with that abundance we 

 behold around us. The different species will vary in their power 

 of multiplying individuals, either from their organization or sur- 

 rounding causes ; and there would also appear in some cases an 

 idiosyncrasy which refuses to perfect their increase or diffusion. 

 I. The value of species is smallest in plants existing in only one 

 or two solitary localities ; such for instance as the cedars of Le- 

 banon, which are indigenous alone in a circumscribed spot, and 

 are so few in number that they can be counted. Many others 

 are extremely local, especially of the OrchidacecE of South Africa 

 and New Holland, which are often only to be met with in the 

 most solitary and secluded spots. The localities of some species 

 of Disa and Serapias at the Cape have become well known from 

 this very circumstance. Thunberg mentions that Codon Roi/eni 

 and Protea nana are both rarities at the Cape ; Origanum Tour- 

 nefortii is alone found on the island of Amergos ; Forstera sedi- 

 folia is a rare plant in New Zealand. These are instances where 

 not only the geographic range is small, but also the amount of 

 individuals. 2. The value is increased in those which have a 

 wide geographic range. Here is included the mass of vegeta- 

 tion, and it comprehends all plants excepting those under the 

 next head. Some have a greater distribution than others ; it is 

 a general rule, that the more simple the organization the greater 

 is the diffusion; hence the frequency with which agamic species 

 are repeated. Aquatic plants have also a wide range; Lemna 

 minor is abundant throughout the northern hemisphere ; Typha 

 latifolia is equally diffused ; also the species of Nymphcea gene- 

 rally, and N. lotus beautifies alike the waters of the Nile and the 

 Ganges. Arundo phragmites, abundant throughout Europe, re- 

 appears in the marshes of the Macquarrie in New South Wales. 

 3. The value is at its maximum in those species, the individuals 

 of which are exceedingly numerous, and are so crowded together, 

 to the exclusion of all others, that they appear to require the so- 

 ciety of each other, and from this latter circumstance have been 

 called social plants. The Gi'aminea are generally social, and in 



