METABOLISM OF COLORLESS PLANTS 51 



are hay and water, but these merely supply the matter and 

 energy for the interplay of various forms of life. Most of 

 these are beyond the scope of unaided vision though chiefly 

 responsible for the obvious changes which occur from day to 

 day in their environment. 



Ordinary tapwater, for instance, contains free oxygen and 

 various inorganic salts in solution, and not infrequently 

 different species of Bacteria, unicellular green plants, and 

 Protozoa. The hay soaking in the water contributes soluble 

 salts, carbohydrates, proteins, etc. It also supplies many 

 microscopic animals and plants which have adhered to it in 

 dormant form and are only awaiting suitable surroundings 

 to assume active life again. 



A microscopical examination of an infusion when it is first 

 made shows very few active organisms, but within a day or 

 so, depending largely on the temperature, it reveals countless 

 numbers of Bacteria which have arisen by division from the 

 relatively small number of dormant and active specimens 

 originally present. At first the Bacteria are fairly evenly 

 distributed in the infusion, but as conditions change, largely 

 through the chemical and physical transformations which 

 they themselves bring about, those species which can employ 

 oxygen in combined form (that is, in chemical compounds) 

 find existence possible and competition less keen at the bot- 

 tom of the beaker, while those types of Bacteria which are de- 

 pendent upon free oxygen gather nearer the surface where the 

 supply is being replenished constantly from the atmosphere. 



Up to this point the life of our microcosm is largely bac- 

 terial unicellular SAPROPHYTIC plants which employ as 

 food the complex decomposition products of the proteins, 

 etc., of the hay. The process is essentially destructive and 

 the simplified products are represented in the relatively 

 simple excretions of the Bacteria. 



