CHAPTER II 



ASSIMILATION OF CARBON AND OF ENERGY BY PLANTS 



WITHOUT CHLOROPHYLL 



§i. General Discussion. — Most plants that are without chlorophyll and are, 

 in consequence, unable to assimilate the energy of sunlight, do not have the power 

 to transform non-combustible inorganic substances into organic compounds. 

 As will appear later, in order to form their various organic substances, green 

 plants require (besides carbon dioxide from the air and water from the soil) 

 nitrogen, potassium, calcium, magnesium, iron, sulphur and phosphorus, all of 

 which occur in the form of various salts in the soil. From the preceding dis- 

 cussion of chlorophyll (see Chapter I) it appears that no plant without chloro- 

 phyll can utilize the energy of sunlight to manufacture combustible organic 

 matter out of such substances. Most non-green plants must use, as sources 

 of both energy and material, organic compounds that have already been 

 formed; they are thus more nearly related to animals than to green plants, as 

 far as their nutrition is concerned. But organic compounds are not the only 

 substances that can be oxidized. This property belongs also to various inorganic 

 substances, such as ammonia, hydrogen sulphide and hydrogen, which thus 

 contain stored energy. As we have previously seen (page xxviii), the heat of 

 combustion of ammonia is greater than that of starch. The researches of recent 

 years have shown that such substances can serve as sources of nutrition for 

 certain plants without chlorophyll. On the basis of their mode of nutrition, 

 plants without chlorophyll may be divided into two groups: (i) plants that 

 derive their energy from organic compounds, and (2) plants that derive it from 

 inorganic substances. 



§2. Assimilation of Energy from Organic Compounds by Plants without 

 Chlorophyll. — Most bacteria, yeasts, fungi and the non-green seed-plants obtain 

 their nutrition from previously formed organic compounds. To study the nutri- 

 tional requirements of these forms, culture media containing various nutritive sub- 

 stances are employed. It was formerly thought that the same nutrient medium 

 should be suitable for all the simpler non-green forms, but this is not so. In 

 higher plants, specialization — i.e., adaptation to surrounding conditions— is 

 accompanied by peculiarities of external form as well as of anatomical structure. 

 On the other hand, the lower plants, such as bacteria and yeasts, are marked by 

 their structural similarity and simplicity. It was supposed, therefore, that such 

 similarity of structure was accompanied by a similarity in the characteristic life 

 processes, and this, in turn, led to the supposition that the nutritive processes must 

 be more or less uniform in these lower forms. The most recent investigations 

 have shown, however, that, in spite of the simple structure of microorganisms 



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