382 NOTES OF A BOTANIST CHAP. 



some bone to pick. They bear on many problems 

 for which there do not yet exist materials, nor do I 

 possess the skill requisite to arrive at a correct 

 solution. On one point only I am pretty clear, viz. 

 that almost every kind of animal now existing in 

 Cisandine Tropical America might find suitable 

 food and lodging on any parallel between the 

 southern tropic and the mouth of the Orinoco ; 

 which is as much as to say that they would find 

 everywhere either the one plant they most delighted 

 to feed on or others which might suit them almost 

 or quite as well. The continual substitution of new 

 forms encountered as we advance in any direction 

 does not, on a superficial view, show much corre- 

 spondence between animals and plants a fact which 

 may be put otherwise, thus : Suppose on a given 

 area at the foot of the Andes every species of some 

 class of animals to be distinct from those of the 

 same class on an equal area at the mouth of the 

 Amazon, it does not therefore follow that every 

 plant is different on the two areas ; we know, 

 indeed, that such is not the case. Yet the modifi- 

 cations that have been and are still in progress 

 among vegetable forms must have some corre- 

 spondence with those that take place in animals ; 

 for all the realms of Nature act and react on each 

 other. The atmosphere and the earth (with its 

 productions, animal and vegetable) are continually 

 giving and taking ; and as their actual relations to 

 each other vary more widely at different points 

 along the equatorial belt than elsewhere on the 

 earth's surface, it is plain that what seems equili- 

 brium is either oscillation or progress in some 

 direction. If plants were the only organic exist- 



