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; after 

 thejr had passed from this control they would be dead. Bo- 

 fore they had been organized and after they had ceased to 

 bear the marks of organization we should call them inorganic. 

 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 preeminent 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 cUamond conchtion 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 preeminent for the stability of its compounds, and 

 for the activity it shows in combining; while nitrogen, simi- 

 larly gaseous, is in marked contrast as l)eing most chfficult 

 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- 

 l;)incr, and the most inert; the easiest to displace, and the 



