Given the following descriptions, identify the option which is incorrect about  slime molds:
P. The slime molds cause the decay and decomposition of the organic matter in the soil.
Q. They play an important role as primary producers in the food web
R. Slime mold leaves a slimy material along the pathway of their locomotion
S. The Plasmodia of slime molds are an excellent material for the study of the structure and physiology of protoplasm.