268 THE PHILOSOPHY OF BIOLOGY 



for the continued existence of the plants themselves. 

 The result of the metabolism of the bacteria is the 

 break-down of this accumulation of such compounds 

 as carbohydrates, and the replenishing of the stores 

 of carbon dioxide and nitrogenous mineral substance 

 on which the plant depends. If bacteria are present, 

 the life process becomes a reversible one. 



Plant life and bacterial life are thus complementary 

 to each other, for, on the whole, the energetic processes 

 of the green plant proceed in the opposite direction to 

 those of the bacteria. An organic world consisting of 

 green plants and bacteria would therefore be one 

 capable of permanent existence. Now, so far, we need 

 only consider these various kinds of organisms as living 

 protoplasmic substances in which energy-transforma- 

 tions of different types proceed. The bacterium is 

 simply a cell containing a nucleus, and the green plant 

 need only be a nucleated cell containing a chlorophyll 

 plastid : this is, indeed, all that it is in the case of a 

 Diatom or a Peridinian. The morphology of the green 

 plant is only accessory to the chlorophyllian apparatus. 

 Neglecting the reproductive apparatus, the higher green 

 plant consists essentially of the chlorophyllian cells in 

 the parenchyma of the leaf, for roots and stomata are 

 only organs for the absorption of water and mineral 

 salts from the soil and carbon dioxide from the atmo- 

 sphere ; while the tissues of the trunk, stems, and 

 branches are, in the main, apparatus for the conduction 

 of these raw materials through the body of the plant, 

 and, of course, the nutritive substances into which they 

 are elaborated. All the innumerable variations of 

 form in the plant (apart from the structure of the 

 flower or other reproductive organ) are adaptations 

 which provide for the absorption and distribution of 

 these substances ; or for the mechanical support of 



