183 



mate solely, or by the distribution of tempera- 

 ture, which we observe in the present state of 

 our planet ; but that this difference of climates 

 leads us to perceive, why a given type of organ- 

 ization develops itself more vigorously in such 

 or such local circumstances. We can conceive^ 

 that a small number of the families of plants, 

 for instance the mu&aceae and the palms, can- 

 not belong to very cold regions, on account of 

 their internal structure, and the importance of 

 certain organs*; but we cannot explain why 

 no one of the family of melastomas vegetates 

 north of the parallel of thirty degrees, or why 

 no rose-tree belongs to the southern hemi- 

 sphere. Analogy of climates is often found in 

 the two continents, without identity of produc- 

 tions. 



The Rio Vichada (Bichada), which has a 

 small raudal at it's confluence with the Oroo- 

 noko, appeared to me, next to the Meta and the 

 Guaviare, to be the most considerable river 

 coming from the west. During the last forty 

 years no European has navigated the Vichada. 

 I could learn nothing of it's sources ; they rise, 

 I believe, with those of the Tomo^ in the plains 

 that extend to the south of Casimena. It ap- 

 pears to me at least not to be doubtful, that the 

 most ancient missions were founded on the 



* The frondes, so important from their size, would not re- 

 sist, vigorous cold. 



