In the animal economy there are analogies with outward nature. Thus respiration is a kind of combustion. Life itself is a kind of fire which goes out when it has no fuel to feed upon. The foliage of a tree has functions like those of the lungs of an animal. Darwin has noted the sleep of plants and their diurnal motions. Dr. Holmes had a bold fancy that trees are animals, with their tails in the air and their heads in the ground; but there is nothing in the trunk and branches of a tree analogous to a tail, though there is a sort of rudimentary intelligence in the root, as Darwin has shown. We use the tree as a symbol of the branching of a family; hence the family tree. But the analogy is not a true one. The branches of a family multiply and diverge when traced backward the same as forward. You had two parents, they had four, these four had eight, and so on. If the human race sprang from one pair, then are its branchings more a kind of network, an endless multiplication of meshes. All the past appears to centre in you, and all the future to spring from you. We get the family tree only by cutting out a fragment of this network. There is little doubt that certain natural laws pervade alike both mind and matter. The law of evolution is universally operative, and is the key to development in the moral and intellectual world no less than in the physical. We are probably, in all our thoughts and purposes, much more under the dominion of universal natural laws than we suspect. The will reaches but a little way. I have no doubt that the race of man bears a definite relation to the life of the globe,--that is, to its age, its store of vitality; that it will culminate as the vital power of the earth culminates, and decline as it declines. Like man, the earth has had its youth,--its nebulous, fiery, molten youth; then its turbulent, luxuriant, copious, riotous middle period; then its placid, temperate, ripe later age, when the higher forms emerge upon the scene. The analogy is deep and radical. The vital energy of the globe was once much more rampant and overflowing than it is now; the time will come when the pulse of the planet will be much feebler than it is now. Youth and age, growth and decay, are universal conditions. The heavens themselves shall wax old as doth a garment. Life and death are universal conditions, and to fancy a place where death is not is to fancy one’s self entirely outside of this universe and of all possible universes.