24 THE CELL 



and Schneidewind isolated a N-combining Bacillus which in sixty-two days 

 transferred 4.6-8.5 mg. of atmospheric nitrogen to proteid nitrogen. Accord- 

 ing to Kuhn one hektar of his experiment field in one year would experience 

 through the agency of microbes alone an increase in nitrogen of 66 kg. Other 

 microorganisms capable of fixing nitrogen are the Azobacteria studied by 

 Beyerinck. Still others which form on roots of certain species of Leguminosae 

 peculiar excrescences, called root tubercles, have the power of transforming 

 free nitrogen into such compounds (amides?) as are able to serve not only 

 themselves but also their hosts as the immediate source of nitrogenous food 

 (Hellriegel) (Fig. 18). 



Several other mineral constituents are needed in the development of plants, 

 notably: iron, which is necessary for the formation of chlorophyll; potassium 

 and magnesium, which it is believed play an important role in assimilation and 

 the syntheses of the body; calcium, which is very important in the transporta- 

 tion and combination of the harmful products of metabolism (oxalic acid), etc. 

 On the other hand, the plant does not require any organic foodstuffs. If the 

 root of a maize plant which has been germinated in water be placed in a vessel 

 with an artificial nutrient solution (one per cent potassium nitrate, 0.5 per 

 cent each of sodium chloride, calcium sulphate, magnesium sulphate, and cal- 

 cium phosphate, and 0.005 per cent ferrous sulphate) while the foliar part is 

 exposed to the air, the plant grows quite perfectly, develops into a large maize 

 stalk, puts forth leaves and brings forth seed. 



Only the plants containing cliromopliyll 1 have the power of feeding ex- 

 clusively on purely inorganic substances. The parts of the plant devoid of 

 chlorophyll receive their carbohydrates from the parts which contain chloro- 

 phyll. Those plants which, like the Fungi, contain no chlorophyll at all must 

 obtain substances already completely organized for their food; and this is 

 likewise the case with the whole animal kingdom. 



The beginning of the organic syntheses going on in nature is therefore 

 the formation of starch in the green parts of plants under the influence of 

 sunlight. The energy stored up by this means is used in all the further proc- 

 esses of the plant body. In plants and plant parts lacking chlorophyll as 

 well as in animals all the life processes take place at the expense directly 

 or indirectly of the substances formed in the green parts of plants. The 

 green plants therefore constitute a necessary condition for the life of all other 

 living beings on the earth. But since carbon dioxide, the nitrates and sul- 

 phates required by plants are present on the earth and in the atmosphere 

 entirely independent of the life processes of animals, plants can get along 

 without the aid of animals. 



We are not to suppose, however, that synthetic processes do not take place 

 in animals. It is true that animals cannot form complex compounds out of 

 completely oxidized carbon (C0 2 ) and hydrogen (H 2 0) and that the animal 

 body can utilize as raw material only compounds of relatively complex consti- 



1 This term, employed by Engelmann, and adopted by the author, includes all the 

 coloring matters in plants capable of exercising an assimilative function. Since, however, 

 by far the most abundant coloring matter is chlorophyll, it will avoid confusion perhaps 

 to use only the one term hereafter. ED. 



