FERMENTATION OF POLYSACCHARIDES 223 



show that each individiual cell has its own separate cell wall 

 made up of cellulose, and that there is a binding material 

 between the two cellulose walls holding the cells together in 

 the form of a tissue. In some plants this middle lamella is 

 relatively thick. In other cases it is thin and can be 

 demonstrated only with some difficulty. Microorganisms 

 of several kinds are known which are capable of producing 

 the enzyme pectinase which softens and dissolves this pectin, 

 thus allowing cells or groups of cells to fall apart. 



Bacteria capable of producing pectinase are of consider- 

 able importance in certain plant diseases. The disease soft 

 rot or black rot of cabbage may be used as an illustration. 

 In this disease the bacteria gain entrance to the tissues of 

 the leaf through the \vater pores or through insect injuries. 

 They begin to grow in the intracellular spaces, producing 

 the enzyme pectinase which diffuses between the cell walls, 

 softens and removes the pectin, and the cells no longer are 

 joined together into a tissue. Microscopic examination of 

 rotting or rotten wood, for example, will show that the 

 cells are no longer joined together and they may be readily 

 separated from each other. 



A practical utilization of this property of pectinase 

 formation by microorganisms is to be observed in the 

 process known as retting. The long cellulose bast fibers of 

 the flax plant and of the hemp plant are used largely in 

 textile industries in the manufacture of linen and hemp 

 articles. In the mature plants the bundles of bast fibers are 

 so closely united to other plant tissues that it is not prac- 

 ticable to remove them and clean them by mechanical 

 means. In order to soften the middle lamella the plants 

 are subjected to the process known as retting. It may be 

 noted that this is the old English form of the word rotting. 

 Literally the plants are rotted for a given length of time. 

 The process of retting may be either anaerobic or aerobic in 

 nature. In the former the bundles of flax or hemp are 



