310 PHYSIOGNOMY OP PLANTS. 



flowering plants must be sought for in tropical countries, and in the 

 latitudes from 12 to 15 distant from the tropics. 



It has appeared to me not unimportant to show the imperfect state 

 of our knowledge in this still little cultivated department of arith- 

 metical botany, and to propound numerical questions in a more dis- 

 tinct 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 belonging to one of the great families of phanerogamous or 

 flowering plants, we should learn thereby at the same time, approxi- 

 matively, the entire sum of all such plants (including all the families). 

 As, therefore, 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 reciprocally limit each 

 other in conformity with still undiscovered laws of universal organi- 

 zation, we approach continually nearer to the solution of the great 

 numerical problem of organic life. But is the number of organic 

 forms itself a constant number ? Do new vegetable forms spring 

 from the ground after long periods of time, while others become 

 more and more rare, and at last disappear ? G-eology, by means of 

 her historical monuments of ancient terrestrial life, answers to the 

 latter portion of this question affirmatively. "In the Ancient 

 World," to use the remark of an eminent naturalist, Link (Abhandl. 

 der Akad. der Wiss. zu Berlin aus dem Jahr 1846, s. 322), "we 

 see characters, now apparently remote and widely separated from 

 each other, associated or crowded together in wondrous forms, as if 

 a greater development and separation awaited a later age in the 

 history of our planet." 



