THE NUTRITION OF HETEROTROPHIC PLANTS 189 



principal agreement with autotrophic plants lies, in the first instance, in the 

 nature of the reserve substances. In addition to nitrogenous we also find 

 non-nitrogenous reserves in Fungi, and among these the fats are especially 

 widely distributed ; on the other hand, since chromatophores are entirely 

 absent, Fungi form no starch. In regions where temporary or more per- 

 manent storage of carbohydrates might be expected to take place we 

 frequently find starch replaced by glycogen, a substance which occurs in 

 animals also. In yeast-cells glycogen (Laurent, 1890, Meissner, 1900) is 

 formed often in considerable quantity from the sugar present in the nutritive 

 solution, and also apparently from various organic acids. Its accumu- 

 lation in organs which are capable of growing in length with great activity in 

 a short time, e.g. the stipe of Phallus (Clautriau, 1895), is especially remark- 

 able ; during this growth glycogen is altered just in the same way as starch 

 would be under similar conditions in the stems of Phanerogams, in order to 

 provide material for the formation of cell-walls. 



Glycogen in its composition is closely related to starch, but it is soluble 

 in water. Its large molecule makes it incapable of diffusing through either 

 protoplasm or cell-wall, and it is for that reason well adapted to act as a reserve 

 substance. It cannot wander from cell to cell ; it must first of all be trans- 

 formed into sugar by means of some enzyme related to diastase. It cannot be 

 employed directly as a nutrient by yeast, since the enzyme cannot be excreted 

 from the cell. 



It is unnecessary for us to discuss the other metabolic processes in the 

 fungus cell since, as we have said, they agree entirely with the corresponding 

 processes in autotrophic Phanerogams. 



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