THE PLANT AND ITS FOOD 27 
when it will withstand complete desiccation. 
When it is grown in water containing traces of 
available nitrogenous food it is green, thrives, 
and multiplies rapidly, but if the supply 
of nitrogenous food is used up, the rate of 
increase drops, and the plants change colour, 
owing to the degradation of the chlorophyll 
and the corresponding development of a 
reddish pigment. When it has reached this 
condition the addition to the water of a small 
supply of nitrogenous food, such as a crushed 
fly, rapidly brings about the restoration of 
the green colour in the cells. When found 
growing on snow-slopes, the red tint is 
obviously due to the absence of available 
nitrogenous food, possibly coupled with the 
conditions of intense illumination and low 
temperature prevailing in such situations, for 
when the plant is once more suitably nourished 
the green colour soon re-appears. 
To sum up, then, what we have learned of 
the significance of chlorophyll, both to the 
plant and to the world at large, we may say 
that its primary function is to enable its 
possessor to synthesise important complex 
foodstuffs from very simple raw materials; 
in other words, that a part of the energy 
contained in the sunlight is rendered available 
for the use of the plant. Furthermore, that 
the sugars or their representatives thus 
formed, provide the starting-point for still 
other reactions which go on within the body. 
They more directly supply the energy which 
