The growth of the cellular slime mold, Polysphondylium pallidum, was studied on a semidefined medium in shaken suspension . When the medium contained large quantities of particulate material, growth was more rapid and the cellular size and protein content were smaller than when growth occurred on a medium containing less particulate material . The cellular levels of DNA, RNA, and protein ; of lysosomal enzymes (acid phosphatase, acid proteinase) ; and of peroxisomal enzymes (catalase) were assayed during growth and the subsequent stationary phase that led eventually to encystment . Only DNA remained at a constant cellular level . Encystment of exponentially growing cells could also be initiated by washing them and introducing them into a soluble peptone medium . The rate of encystment was proportional to the osmolarity of this medium . The encystment process was followed with respect to the cellular levels of DNA, RNA, protein, carbohydrates, acid phosphatase, acid (3-N-Acglucosaminidase, and catalase . The most dramatic change occurred in the cellular cellulose content, which increased by at least an order of magnitude by the time encystment was morphologically complete . It was concluded that the encystment of this slime mold in suspension exhibits a number of biochemical similarities to the development of this and other cellular slime molds on a surface .