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 w^ell. 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- 
