1007. The Natural System depends not upon the resemblance of plants in one particular feature, but upon their general resemblance in structure, habits, and qualities. Ray, who appears to have had the first clear idea of a natural system, defines it to be one ' which neither brings together dissimilar species, nor separates those which are nearly allied;' and Jussieu says, that as a species ' consists of individuals very much alike in all their parts, and retaining their resemblances from generation to generation' (Ibid. p. xxv.), so a group of species combined upon the same principle forms a genus, a group of genera an order, and a group of orders a class.
