570 THE PLANT’S PLACE IN NATURE 
ing as it chooses. The materials of such a living boat as we 
have imagined would be continually dissolving into the 
stream; while, at the same time, fresh inorganic material, 
admitted by the indwelling power, would be building the 
structure anew. So long as these materials formed part of 
the boat or showed signs of having once belonged to its 
organized structure, we should call them organic; and we 
should apply the same term to any compounds possessing 
the same properties. So long as the materials were arranged 
in a way to permit the indwelling chooser to act through 
them directly, they would constitute living substance. Until 
thus controlled they would be simply lifeless substances; atter 
they had passed from this control they would be dead. Be- 
fore they had been organized and after they had ceased to 
bear the marks of organization we should call them inorganie. 
The materials of which these wonderful boats are made 
consist chiefly, as we have seen, of the elements carbon, 
hydrogen, oxygen, and nitrogen. It is perhaps significant 
that each of the four is preéminent for certain properties 
which are in marked contrast with what characterizes one 
or more of the others. Carbon, in a sense, is the most solid 
of all known substances. It requires the highest tempera- 
ture to melt it, and in its diamond condition exceeds all 
other materials in hardness. It is remarkable for the dif- 
ferent ways it can combine, and as entering into more com- 
pounds than all the other elements taken together. Hydro- 
gen, on the other hand, is of all common elements the most 
fluid. It requires the utmost cold to freeze it and remains 
gaseous under the highest pressure. It is remarkable for 
the ease with which it may be made to pass from one com- 
pound to another. Oxygen, also a gas at ordinary tempera- 
tures, is preéminent for the stability of its compounds, and 
for the activity it shows in combining; while nitrogen, simi- 
larly gaseous, is in marked contrast as being most difficult 
to combine and most unstable in combination. We have 
here, then, three of the most fluid of substances, gaseous at 
all life-temperatures, combined with the most solid sub- 
stance known; and among the four we find the readiest com- 
biner, and the most inert; the easiest to displace, and the 
