lo PLANT LIFE. 



body is enabled to add to its bulk, or grow, and at the 

 same time to replace those portions of its own living 

 substance that disappear in proportion to the amount of 

 work done, chemical and physical, collectively known as 

 vital energy. Hence it follows that one important factor 

 in determining the presence or absence of life at any given 

 spot, would consist in the presence or absence of food 

 material under a form suited to the requirements of life. 

 Keeping in view the well-known fact that different forms 

 of life require different kinds of food, chemically con- 

 sidered ; and further, that the physical condition of the food 

 is also of importance, we gain a further insight as to the 

 conditions that determine the presence of a given group 

 of organisms at any particular spot. As an illustration of 

 the above statement, assuming for the moment food to be 

 the only factor in determining the distribution of life, we 

 should find that a moss could live under conditions where 

 it would be absolutely impossible for a fungus to do so 

 for the following reasons. The food of a moss plant 

 consists of inorganic matter, that is, matter whose existence 

 in Its present condition is not directly due to life; carbonic 

 dioxide, derived from the atmosphere, and water along with 

 small portions of various substances derived from the soil 

 dissolved in it, and absorbed by the root of the moss, 

 furnish it with all the chemical elements which its own 

 vitality enables it to rearrange and convert into its own 

 substance. A fungus, on the other hand, does not possess 

 the power of decomposing and utilizing inorganic matter 

 as food, but can only feed on organic matter, that is, matter 

 that owes its present chemical composition to the direct 

 action of life ; consequently, other things being equal, the 

 moss has the choice of a much wider range in which to 



