30 OUTLINES OF EVOLUTIONARY BIOLOGY 



side by side, and that the complex undulatory movements are 

 due to alternating contractions and relaxations of these. 



The presence of a firm cell-wall makes the protrusion of 

 pseudopodia in the case of Haematococcus quite impossible, and 

 at the same time prevents the organism from taking in any 

 solid food, for there is no aperture through which such food 

 could pass. It must therefore depend entirely for its food supply 

 upon substances which are able to pass through the cell-wall 

 in a state of solution. These substances are all very simple 

 chemical compounds, consisting of certain mineral salts and 

 carbon dioxide gas, which, amongst them, contain all the elements 

 necessary for the formation of protoplasm. They are, however, 

 very stable bodies, with little or no affinity for oxygen gas and 

 little potential energy. They cannot, therefore, by themselves 

 supply the energy which the organism requires for its vital 

 activities. Energy has to be supplied from the environment 

 and the simple food materials thereby partially deoxidised and 

 combined together in more complex and less stable molecules 

 containing stores of potential energy which can be liberated by 

 oxidation as required. 



The energy which Haematococcus uses for the building up of 

 its complex molecules is, as we have already observed for green 

 plants in general, the radiant energy of the sun, in the form of 

 light. The process is known as photosynthesis, and can only 

 take place in organisms which possess chlorophyll or some 

 functionally equivalent pigment, such as hacmatochrome. In 

 some way or other the pigment absorbs the energy of the light 

 rays and renders it available for the process of constructive 

 metabolism (which in plants is also spoken of as assimilation). 



The first step in this complex process involves a chemical 

 decomposition, carbon dioxide, obtained in solution from the 

 surrounding water, being decomposed with evolution of free 

 oxygen gas. 



We have already seen that in the combustion of charcoal 

 the reverse of this takes place, carbon and oxygen combining 

 to form carbon dioxide and the act of combination being accom- 

 panied by the liberation of energy. It is obvious that if energy is 

 liberated in the one process a corresponding amount must be 

 absorbed in the other. 



When a glass jar of water containing Haematococcus, or any 

 green aquatic plant, is placed in bright sunlight the decomposition 



