184 VEGETABLE PHYSIOLOGY 
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 protein and fatty bodies. 
Others need the nitrogen to be supplied in the form of 
amino- or amido-acids, as they have no power to utilise 
the simpler ammonium salts; others again need their 
proteins as well as their carbohydrates to be supplied to 
them as such, for they possess scarcely any constructive 
ability. ’ 
A similar power of utilisig 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 synthesis of proteins also may be shortened by sup- 
plying the roots with material such as asparagin, leucin, 
or urea. Protein 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 
