78 PLANT-ANIMALS [CH. 



observations on animals which had been kept for a 

 month in darkness in pure sea-water, certain individuals 

 were discovered which had so far condescended from 

 this ascetic mode of life as to have become cannibals. 

 Instead of being straight and slim, they carried a 

 large pouch-like distension about the middle of their 

 bodies. Microscopic examination showed that the 

 pouch was occupied by another adult Convoluta as 

 large as that which had engulfed it. Hence it follows 

 that normal adult C. roscoffensis in its natural state 

 does not refrain from food because it cannot swallow, 

 but because it does not want to eat. 



Now green plants do not take up solid food : they 

 manufacture it. From inorganic substances, water 

 and carbon-dioxide, which are absorbed from without, 

 the green cells of plants manufacture sugar. This pro- 

 cess, which is a preliminary to nutrition, is termed by 

 botanists, photosynthesis, since the energy required 

 for the manufacture of the carbohydrate (sugar) is 

 derived from the radiant energy of the sun. The 

 green pigment, chlorophyll, which is associated 

 in the green cells of the plant with specialised, 

 granular bodies called chloroplasts, absorbs light, 

 and in some way, as yet imperfectly understood, this 

 radiant energy is utilized by the protoplasm of the 

 chloroplasts in the manufacture of sugar. The plant 

 possesses also the power of synthesising yet more 

 complex substances. Beside carbohydrates such 



