178 THE PHYSIOLOGY OF EARTHWORMS 



This has been explained by Mangold (1951) on a basis of taste 

 selection. He took pine needles, which could be easily drawn into 

 burrows because of their shape, boiled them to remove their 

 characteristic flavour which is not attractive to earthworms, and 

 then coated them with gelatine containing finely powdered litter of 

 various other leaves in suspension. From the rate at which such 

 preparations were consumed Mangold concluded that when the 

 litter was fresh, beech was the most favoured food plant, followed 

 by maple, oak, horse-chestnut, lime, willow and false-acacia. If 

 decaying leaves were used the order changed and became willow, 

 false-acacia, oak, lime, beech, maple and horse-chestnut, indicating 

 that probably the breakdown processes in the leaves change the 

 acceptability of the leaves to the earthworms. There is also a 

 possibility that maturation in the accumulation of polyphenols may 

 be important (Satchell, personal communication). 



Wittich (1953) in field experiments on naturally fallen and 

 decayed litter found a diff"erent order of acceptance and explained 

 this partly on a basis of the physical texture of the leaves, and 

 partly on the presence of unpleasant substances in fresh leaves, 

 such as beech, which break down as decomposition proceeds. As 

 the inimical substances are removed from the leaves by leaching 

 and decomposition so the order of leaf acceptance changes and the 

 earthworms begin to graze on leaves ignored when freshly fallen. 

 After chemical analysis of the leaves from various trees Wittich 

 suggests that protein content, a measure of food value, is impor- 

 tant to the order in which the leaves are eaten, but he does not 

 suggest that the leaf proteins can be detected by the earthworms. It 

 is possible that the protein content is correlated with some sub- 

 stance which can be detected by chemoreceptors. 



Mangold (1953) extended his observations on the plants eaten by 

 earthworms to include synthetic chemicals such as alkaloids, 

 sugars and acids. He used the same experimental method as before 

 including the known chemicals in the gelatine covering pine needles. 

 Alkaloid substances are not taken by earthworms above a certain con- 

 centration, 50% acceptance being noted at a concentration of 0-01 g 

 in 20 g gelatine, but concentration greater than this was greeted by 

 complete rejection. Low concentrations of a number of acids often 

 found in plant materials, e.g. phosphoric, tartaric, citric, oxaHc 

 and malic acids, were accepted but not high concentrations of 



