124 PHYSIOGNOMY OF PLANTS. 



countries, and in the latitudes from 12 to 15 distant from 

 the tropics. 



. It has appeared to me not unimportant to show the im- 

 perfect state of our knowledge in this still little cultivated 

 department of arithmetical botany, and to propound nume- 

 rical questions in a more distinct and determinate manner 

 than could have been previously done. In all conjectures 

 respecting numerical relations we must seek first for the 

 possibility of deducing the lower or minimum limits ; as in 

 a question treated of by me elsewhere, on the proportion of 

 coined gold and silver to the quantity of the precious metal 

 fabricated in other ways; or as in the questions of how 

 many stars, from the 10th to the 12th magnitude, are 

 dispersed over the sky, and how many of the smallest 

 telescopic stars the Milky Way may contain. (John 

 Herschel, Results of Astron. Observ. at the Cape of Good 

 Hope, 1847, p. 381.) We may consider it as established, 

 that if it were possible to know completely and thoroughly 

 by observation all the species bel 'ngiiig to one of the great 

 families of phanerogamous or flowering plants, we should 

 learn thereby at the same time, approximative^, the entire 

 sum of all such plants (including all the families). As, there- 

 fore, by the progressive exploration of new countries we 

 progressively and gradually exhaust the remaining unknown 

 species of any of the great families, the previously assigned 

 lowest limit rises gradually higher, and since the forms reci- 

 procally limit each other in conformity with still undis- 

 covered laws of universal organisation, we approach continually 

 nearer to the solution of the great numerical problem of 



