5. PLANT LIFE
The plants are of the carbon-metabolism, silicate-shell type, like the primitive animals. They spread out from the equator as far as they could go before the baking polar summers killed them. They have normal seasonal growth in the temperate zones and remain dormant and frozen in the winter. At the poles there is no vegetation, not because of the cold winter, but because of the hot summer. The winter winds frequently blow over dead trees and roll them as far as the equatorial seas. Other dead vegetation, because of the highly silicious water, always gets petrified unless it is eaten first. What with the quartz-speckled hides of the living vegetation and the solid quartz of the dead, a forest is spectacular.
The silicone animals live on the plants. They chew them up, dehydrate them, and convert their silicious outer bark and carbonaceous interiors into silicones for themselves. When silicone tissue is metabolized, the carbon and hydrogen go to CO2 and H2O, which are breathed out, while the silicone goes into SiO2, which is deposited as more teeth and armor. (Compare the terrestrial octopus, which makes armor-plating out of calcium urate instead of excreting urea or uric acid.) The animals can, of course, eat each other too, or make a meal of the small carbonaceous animals of the equatorial seas.
Further note that the animals cannot digest plants when they are cold. They can eat them and store them, but the disposal of the solid water and CO2 is too difficult a problem. When they warm up, the water in the plants melts and can be disposed of, and things are simpler.