OTHEK METHODS OF OBTAINING FOOD 197 



because in them there is no chlorophyll apparatus, and 

 hence constructive processes must be very rudimentary. 

 Distinct differences can be seen, however, in this group. 

 Certain lowly forms appear to be able to utilise very 

 different compounds of carbon and to synthesise carbo- 

 hydrates therefrom. Many can grow and multiply in 

 solutions of simple acids such as formic or acetic. A much 

 larger number need for their nutriment a supply of carbo- 

 hydrates in the form of sugar, and if this is given them, 

 together with certain relatively simple compounds of 

 ammonia, especially ammonium tartrate, they can con- 

 struct therefrom proteid and fatty bodies. 



Others need the nitrogen to be supplied in the form of 

 amido-acids, as they have no power to utilise the simpler 

 ammonium salts ; others again need their proteids as well 

 as their carbohydrates to be supplied to them as such, for 

 they possess scarcely any constructive ability. 



A similar power of utilising carbohydrates and allied 

 bodies is exhibited by many green plants. If their roots 

 are watered with a solution of sugar, they can take it up 

 and economise by its aid the sugars which the chlorophyll 

 apparatus is constructing. Various bodies also from which 

 sugar can be formed are absorbed when presented to 

 the roots, and serve as forerunners of sugar in the plant. 

 Among these may be mentioned Glycerine. The process 

 of the S} 7 nthesis of proteids also may be shortened by sup- 

 plying the roots with material such as asparagin, leucin, 

 or urea. Proteid as such can only be utilised by a few 

 flowering plants which possess special mechanisms for its 

 preliminary digestion. 



Among what we must regard as these abnormal methods 

 of food supply we must include certain processes in which two 

 organisms are associated, for the well-being, in some cases, 

 of both, in others for that of only one. The two organisms 

 are brought into very intimate relationships with each 

 other, in some cases a very complete union of their tissues 

 being effected, so that transport of elaborated food materials 



