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Growth of this type occurs when the material afded contributesto the growth potential of the organism. Thus, the sizes of growth increments increase 39 D. S. Mitchell within equal time periods,as growth continues,and it is more realistic to calculate relative growth rate (RGR),which is defined as the increase of material per unit of material present per unit of time,rather than growth rate (GR),which is simply the increase of plant material per unit of time and does not take into account the quantity of material present.

On the other hand pistia, a free-floating,rosetteforming macrophyte has a smaller fauna (4,314individuals) consisting mostly of predators. One would expect the above results,since floating macrophytes tend to shade out phytoplankton and submerged macrophytes,resulting in an environment which is not acceptable to herbivorous species. Mud species increased from 28 35 J. J. This change involved the appearance of 21 species new to the area, and a disappearance of 3 species. Salvinia did support a large predator population (10species) in the dissected leafmass which hangs down under the floating leaves.

Emergent plants also provide the rather special conditionsneeded by swamp inhabitants,such as the swamp worm, Alma enzini. In such swamps,Alma digests large amounts of detritus. Emergent macrophytes often provide extensive areas of plant cover above water. In papyrus swamps,each papyrus stem is terminated by a large umbel with many long rays. Thornton (1957) found each umbel supported a fauna which was strongly correlated with umbel development. Another emergent,Phragmites australis, serves as a host for the parasitic smut fungus,Ustilago grandis, in addition to other plant and animal pests (Durska, 1970).

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