FRIENDS AND ACQUAINTANCES 71 



produced abundance of seed annually ready to fill up all 

 vacancies caused by death, could (metaphorically) laugh at 

 all such enemies, and let them devour as they pleased. Such 

 a plant is our own oak tree, which, though infested by galls 

 of many kinds and devoured by numerous caterpillars, is 

 yet not in the least danger of extinction by them, and there- 

 fore has developed no special protection against them. 



Again, when in any one year much injury is done by 

 caterpillars, that affords such an increase of food to young 

 birds that the insects are almost all destroyed, and in the 

 following year there are comparatively few, giving the trees 

 time to recuperate and attain to their former vigour ; while 

 in the following year the birds have less food and are thus 

 diminished in numbers. This wonderful action and reaction 

 of all living things on each other is beautifully described 

 by Mr. Hudson in the chapter of his " Naturalist in La Plata," 

 entitled " A Wave of Life." 



Early in 1879 I read Grant Allen's book on the " Colour 

 Sense' (for the purpose of a review in Nature), and wrote 

 to Spruce asking for some information as to the colours of 

 edible fruits in the South American forests. His reply was, 

 as usual, full of interesting and suggestive facts, and I here 

 give it. 



" To reply fully to the queries in your last letter would 

 require me to wade through several volumes of my MSS., 

 but I have put together a few excerpta which may serve your 

 present purpose, if they only reach you in time. 



" I fear I cannot adduce much evidence as to the fruits 

 most sought after by birds and monkeys. I have seen birds 

 feed on various fruits, but on scarcely any that were not food 

 for man — or at least for Indian man — although a few of 

 them might be too austere, or too acid, for my taste. If, 

 as Sterne says, ' dogs syllogize with their noses,' so do birds 

 with their beaks, monkeys and Indians with their teeth : 

 insomuch as relates to the choice of food. In my long 

 voyage on the Cassiquiare, Alto Orinoco, and some of their 

 tributary streams, my Indians met with many fruits new to 



